I just bought one off Soviet with a Radeon 7000. Now to save up and buy that X500 case.
My advise though, unless you want to see how low end a machine MorphOS can run on...
I'd hold out for the official G5 support and get one of those. Or if that is out of your price range, get an iMac with 64Mb of vRAM. Avoid the eMachine and anything with only 32Mb of vRAM!