Goodwill Computer Works in Austin, TX carries both PC and Macintosh parts as well as systems and barebones.
It’s great! Last I checked, you could still find PPC Macs there, mostly Sawtooth G4s, but they’re fully refurbished and tested, and typically crammed with as big a hard disk and as much RAM as they can put into them, and for about $100, which is roughly equal to what I see some places selling stock-configuration units for on the interwebs.