I had 2 C-64s just freeze up and die on me back in the late 80s'. I ended up buying an aftermarket power supply from a local C64 dealer in Phoenix @ 1988. I still have the power supply and my 3rd C-64 is still going strong. I have a boxed C-64c that I'd bought from Rick Stillwell on this site. It works, but I have a feeling that it has a capacitor, or 2, that are going bad.
I've seen VIC-20 and C-64 carts being sold at Half-Price-Books in Dallas. The last cart I'd bought from them was Radar Rat Race, which isn't really that great of a game. I already had a copy of that game on floppy, but I bought it anyways.