Ryan,
No doubts about it, if you are looking for bang for the buck performance and TONS of Mod options. Aftermarket parts like no other car in the world.......... Well, I have to say there is only one car to consider....... Not that I am biased or anything but.....
OK you beat it out of me.... 90-94 Mustang GT or LX.

Can be had for 1-5k depending on miles and condition. You can spend a few thousand have a really nice FAST car for cheap. Parts are cheap and VERY plentiful unlike the RX7. Not to knock the RX, as they are also a fine car.
Just my .02
Cheers,
Volcano God