I don't think classical music
recordings are 100% free though. The arrangements may be public domain, but they still have to be performed and recorded, and therefore licensed by PD. Although, surely it's much cheaper than pop music. Unless you were thinking MIDI.
As others have suggested, I just hope we have more customization of the various events in the game that trigger music, like the shops and car introduction. Make all of the music replaceable by our own, and I don't think anyone can object to it.