The New York Times > Arts > Music > The Most Expensive Album Never Made:
[Axl] Rose began work on the album in 1994, recording in fits and starts with an ever-changing roster of musicians, marching through at least three recording studios, four producers and a decade of music business turmoil. ... Along the way, he has racked up more than $13 million in production costs, according to Geffen documents, ranking his unfinished masterpiece as probably the most expensive recording never released.
This is actually a fascinating read, whether you like Guns'n'Roses or not.