Do-it-yourselfers might bet they can fix the G5 and turn it over for a profit, other interested parties would just want the case and innards. Either way, if the machine is currently broken I don't think you could even get $100 for it.
I am in a similar situation. I have a long-unused, working-but-flaky Powermac G4 minitower (circa 1999 or so) gathering dust in my closet. I mothballed it because it used to occasionally but randomly shut off, probably a bad logic board or power supply. Too expensive to have fixed & the only people interested in it would want it would either fix themselves or scavenge for parts. I also have the Apple 17" Studio Display monitor that went with it -- it had
that old proprietary connector that only worked with those minitowers. The computer is potentially fixable, and the monitor still works great, but I'd be happy at this point to get $100 for it, but I have no idea if anyone would even want that machine+monitor for that price....