Does anyone know of any good sites to browse cars to buy that aren't stock? Those that have been mod'd or whatever? Ebay I tried already and got about 72 hits for cavys, but only about 4 or 5 were mod...

Try the local public auction. Have seen some modded there and you can get them cheap. I just got a 1992 Cavalier with 68,000 original miles for $1800. Car was in such good condition I couldn't believe it. Only problem was the typical early 90s clear coat paint peeling problem. Mechanically it is like new. Worth a try anyway if you have a public auction near you.