Danny Elfman, the Los Angeles Philharmonic, the International Contemporary Ensemble. They're just a few of the classically trained musicians jumping on the video game bandwagon lately to make absurd amounts of cash.
Just how absurd?
Game composer and Game Audio Network Guild founder Tommy Tallarico tell the Minneapolis Star-Tribune that the typical fee for a composer is US$1,000 per minute of music, sometimes upwards of US$2,000. When most games call for one to two hours of music you're talking about composers pulling in US$60,000 to US$240,000 for a single game.
I'm not sure how that compares to total budget, but I think the mood-setting music of games like BioShock and Prince of Persia and Killzone 2, is well worth the price. It helps shape the experience.