Nova... Yes I know what you are thinking. There is someone with one on SSS purely for track days and it will keep up with an Evo lol. He has put a different engine in the back and it's also RWD... Think it cost him a lot to do though.
E30... Cheap as chips as mainly they have a lot of rust in places you don't want but, if it's going to be a track car, you'll probably have it strengthened anyway.
How about an old sierra, capri, astra, vectra... There is a lot of possibiliies. If I was to build a track car though, I think I would go for a westfield with a busa engine lol.
Also, the E30 touring is suppose to make a good track car as they are suppose to have very good weight distribution.