Just as it was normal for a Wright building to cost much more than expected when it was new - three times the original estimate he snared you with was routine - so the guardians of Wright's buildings today face quite startling bills to keep them standing. Between $3m and $8m to restore one of his iconic houses. $10m to renovate one of his youngest university buildings. Another $10m to set right a modest 1909 hotel in Iowa - a sum so steep the local council is trying to sell it on eBay. $24.5m to salvage the Guggenheim's flaky exterior. At least $86m, some say, to rescue the twin headquarters of the Wright cult, his studio-communes of Taliesin, in rural Wisconsin, and Taliesin West, in the Arizona desert. Like the man himself, his creations are very high maintenance. But then, Wright's whole life was an experiment. Because while his architecture pushed at the boundaries of convention, his own life went crashing right through it.

Wright lived a very long and hectic life. He lived it large, at full throttle, from Victorian times to the nuclear age. This little dandified fellow, fond of his stacked heels and capes, his silver-topped canes and fancy hats, his fast cars, thoroughbred horses and dangerous women, once fled the United States with the wife of a client - abandoning his own wife and six children. It might not raise an eyebrow today. But this was not done in the genteel Chicago suburb of Oak Park in 1909. When he returned, unrepentant, a year later, his former friends crossed the street to avoid him. But things got much worse.

In the summer of 1914 he was away from Taliesin (the name means "shining brow", a nod to Wright's Welsh ancestry) supervising the building of the Midway Gardens pleasure park in Chicago. During his absence a deranged servant murdered his lover, Mamah Borthwick, her two children and several guests with an axe, and then burnt the house down. After this horror, Wright rebuilt it. It burnt down again, this time by accident. He lost a valuable art collection, but he rebuilt it again, bigger still. The next Mrs. Wright turned out to be a morphine addict who went mad and died young. But not before setting the police onto Wright, by then deeply in debt. He had gone on the run under an assumed name with a new exotic lover, the Montenegrin-born dancer and mystic Olgivanna, and their illegitimate child. Olgivanna, 30 years Wright's junior, became the third and last official wife. Understandably, the American press came to relish Wright and his escapades. They couldn't make this stuff up.

But he always bounced back. An irrepressible Mr. Toad, a big spender and a master of brinkmanship, he was constantly having to be bailed out. This is despite the fact that from 1932 until his death, he paid none of his staff - instead he worked on an apprentice system, and they paid him. They also had to work in the fields, to cook, to clean. And of course to repair the buildings constantly. Olgivanna organised them in every way, allegedly even down to deciding who should have sex with whom, who should marry whom. The Taliesin Fellowship, as he named it, was an enclosed society, perilously akin to a religious cult. Wright always said that the religion in question was Nature with a capital N. It wasn't. It was a cult of the individual. Him. An architectural prophet with flowing silver locks.

Wright built his western Taliesin in Arizona, home to this growing band of disciples, even as his bank was getting ready to repossess the first one. He got it back, of course. And he spent his clients' money as freely as he spent his own. Small wonder his life inspired a bestselling novel by Ayn Rand and a Hollywood movie - King Vidor's 1949 The Fountainhead, in which Gary Cooper played him as an against-the-world, self-destructive genius ("Howard Roark"), prepared to dynamite his own buildings rather than compromise. It was no stranger than the truth.

Wright was a copper-bottomed maverick and visionary. He never curtailed his huge ambition - or his equally huge ego. In 1956, by then a very old man, he unveiled plans for the world's tallest skyscraper, complete with nuclear-powered lifts, the Mile High. That was never built, though it looks uncannily like the latest generation of supertall 21st century towers. His final masterpiece, in 1959, was the unprecedented white spiral of the Guggenheim, the granddaddy of all today's weird-shaped "signature" buildings by superstar architects. He died six months before it was opened, at the age of 91, busier than he had ever been in his life. His body was carried to its grave from the original Taliesin on a flower-heaped farm wagon. That was how his murdered mistress Mamah had been buried, 44 years earlier.

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The Guggenheim? That would be the same Guggenheim that, despite several major refurbishments since it opened, now needs all those millions spent on it to restore its flaking exterior. As much money, in fact, as it costs to mount six or seven of the museum's renowned annual blockbuster exhibitions. For a building still only in its forties, it has already needed some extensive facelifts. But such is the pulling power of Wright that all the money has already been donated by the museum's wealthy trustees - the lion's share of it given by the former chairman, Peter B. Lewis. "I have always considered this building to be the most important piece of art in our collection," Lewis commented when launching the appeal. Just as well, since the broad internal spiral ramp of the museum's rotunda has always been a nightmare to show art in. But for all his largesse - Lewis had given the museum $77m over 12 years, according to the New York Times - he was not as indispensable as the building he loves. Lewis fell out with the Guggenheim's director, Thomas Krens, over his international expansion plans, and resigned in January this year.

This Wright flagship building has a flotilla of others in its wake, all crying out for cash. Because Wright pushed architecture just as far as it could go, and then some. The clear-sighted vision of genius was not always matched by the technology of his time. Nor was Wright too concerned about the niceties of building, though he designed some exquisite details. The trouble with being ahead of your time is that time has a habit of catching up with you. Expensively.

Some have already been saved from ruin - such as his outrageously daring Fallingwater House of 1937, the most famous modern house in the world. This was originally intended, by its owner Edgar J. Kaufmann, to be a weekend cottage. He wanted it to be built on a favourite family picnic spot, looking across to a waterfall in the Pennsylvania forests. Wright had other ideas. But he did not tell Kaufmann what they were. He did no work on the design. For months and months. Thus began a legend.

Eventually Kaufmann's patience ran out and he telephoned to say he was driving over - a distance of 140 miles. "Come on over, EJ - your house is finished," said Wright calmly, and put down the phone. Everyone in the office knew that not a single line had been drawn. So Wright sat down, got out his coloured pencils and - in two hours flat or as much as three by some accounts - designed the house, in its entirety, down to the smallest detail. As he drew it, he talked, describing it. It was all in his head. Wright placed the house on a great rock right on top of the waterfall. He named it, and signed it. This astonishing feat of speed-design is the single most celebrated act of architectural creativity ever. It really happened: several people witnessed it. If Wright was a kind of deity, this was his kind of miracle. He was in his late sixties by then. Work was scarce, his career was stalling. Fallingwater - a house blending Wright's broad-brimmed Arts and Crafts-influenced Americanism with the white horizontality of the European modernism he professed to despise - instantly turned him back into a star.

Kaufmann was overjoyed - even though, with his house on top of the waterfall, he could not see it as he had asked. "Don't change a thing," said Kaufmann. The house was meant to cost him $35,000. By the time Wright had finished with him, it had cost $125,000. One economy was made, however: He refused to let Wright cover it inside and out with gold leaf.

Fallingwater's problems began right there. Wright balanced the house on the rock, with great optimistic cantilevered concrete floors and balconies stretching out to either side, hovering in the air. Before long, these started to sag. But despite a sobering catalogue of almost continuous repair from the moment it was complete, the house was instantly acclaimed as a masterpiece. By the mid 1990s - by then owned by a state preservation society - the house was on life support. It had sagged so badly it had to be propped up. But in death as in life, Wright always somehow finds the money in the end. Following a complex re-engineering exercise on the house to keep it from collapsing, Fallingwater has been saved. As usual, enough donors came forward. How much was it to repair this Frank Lloyd Wright holiday cottage? A little matter of three million dollars. Per square foot, that makes the $24.5m of repairs just starting on New York's Guggenheim seem cheap.

But it will take at least $5m just to start to fix the enormous - and collapsing - pseudo-Mayan temple of the 1924 Ennis-Brown house, across the continent in the hills of Los Angeles. It has been in trouble for years, because it was one of many buildings designed by Wright using what he called "textile blocks" - concrete blocks moulded with his geometric designs, held in a matrix of steel rods. Wright used textile blocks for nearly 40 years, and never conceded that they were rubbish. Made with little attention to quality control, they soak up water and airborne pollutants, the steel rods inside rust and expand, and they then crack and crumble to dust.

The Ennis-Brown house is, like several other Wright buildings, dissolving in this way. Despite being used as the set for Harrison Ford's character in Blade Runner (and appearing in 59 other movies), despite being championed by film actress and architecture enthusiast Diane Keaton, the future for the house looks gloomy. It had already been shaken in a 1994 earthquake. Then, in March this year, after heavy rains, mudslides hit the area. The house started to shift. Chunks of wall fell off. It had to be evacuated. It looks like this could be the coup de grace. Even the trust which runs the house, with nowhere near enough money for the work, is starting to sound desperate.

As is Mason City in Iowa, which has resorted to putting its semi-derelict Wright-designed hotel, the Park Inn, up for sale on eBay with a price tag of $10m. "We are interested in hearing from people who view it as an opportunity to be involved in saving and restoring this world-class building", they say hopefully.

British architect John McAslan knows all about Wright. He has restored part of the master's Florida Southern College, a Methodist liberal arts campus that is the biggest integrated collection of Wright buildings anywhere. When it was built, budgets were meant to be tight. Many of the buildings used his trademark textile blocks, made by students to pay their way through college. They were, as usual, dodgy. McAslan's recent refurbishment of the last building of Wright's on the campus, the 1950s Polk science building, cost $10m. About 60 per cent of the blocks needed to be replaced or repaired. Even when new, says McAslan, "the Polk building was something like three times over budget and three years late." Situation normal, then. Yet he remains a fan.

"Wright was an amazingly rude and arrogant man, and apparently he smelt rather bad. But he was a remarkable character. A superstar," says McAslan. "To me the problems with his buildings do not devalue his legacy. In a way, it's as if the buildings were never finished. He didn't really care. To him, it was the output that was important."

That phenomenal output - at least 470 buildings built, many demolished over the years, and huge numbers designed but never built - is a growing problem. Now Wright's American torch-bearers, based in the two Taliesins, are facing the biggest crisis of all as the buildings gently subside around their ears. The Frank Lloyd Wright Foundation, which jealously guards the master's reputation, his architecture school and archives, is in trouble. Two chief executives have left in the past year and a new one has yet to be appointed. There are eight unfilled seats on the board. The separate Taliesin Fellowship, now largely comprised of idealistic greybeards, is at odds with the board. As I write this, crisis meetings are taking place.

There is yet another linked organisation, Taliesin Preservation Inc, that has spent $16m patching the campuses up since 1991. A drop in the ocean of what is needed. The original Taliesin, dating from 1911 and a work in progress all Wright's life, is now officially a "Priority One" threatened landmark, one of the most endangered historic complexes in the United States. Just getting the report written into all the work that needs to be done will take two years and cost a million dollars. And there are not very many apprentices around these days prepared to pay the nearly $13,000 annual fees to train under people who unfortunately cannot be Frank Lloyd Wright himself.

So where does Wright's stock stand today? Is he, despite everything, still a god? Terence Riley, chief curator of architecture and design at New York's glittering Museum of Modern Art, is in no doubt that, as ever, he will escape his troubles to glory.

"Right now, I would say his reputation remains justifiably high," says Riley. "Many architects say they are risk takers or experimenters, but few are as audacious as was Wright. That said, anyone who is truly pushing the limits runs the risk of failure, partial or total. A number of Wright's buildings do have problems, but none of them are total failures. And the great majority have no more problems than any building would have after 50 if not a hundred years of use."

For Riley, Wright was a true innovator, and for that, people are prepared to pay the price to keep his buildings going. "It appears to me that there are quite a few people who are willing to forestall the effects of time when it comes to Wright's work. The big problem is not the public structures, where there are larger resources to draw upon, but the single family homes. Even the most devoted and houseproud owners will find the costs to be a considerable burden."

Well, so they always did. And the work of today's architects, in a much more tightly-regulated world, goes wrong often enough too. But none of them has anything like the charisma of Wright. Any smart idea they come up with, the chances are that Wright had that same idea generations back. Why did people tolerate this preening old wizard in his lifetime? Why do they scramble to save his buildings today, even as they wring their hands in despair? That's an easy one to answer. He was just so blindingly good. He was an original.