RX-8.
Faster than an E36, loads cheaper than an E46, and a lot easier on tires than an STi. Seeing the damage that J-Fo's Evo did to my RA-1s in 6 runs at Mineral Wells made me leery about the tire budget for a nose heavy, camber-limited, Macstrut sedan. Come to think about it, that applies to the Bimmers as well. 2800 lbs > 3200+ lbs
They're well balanced, reasonably light, have incredible brakes, and enough power to make them entertaining. You can pick up low mileage ones all day for $15-16k. Add a set of shocks and springs or your choice of coilovers, some 17" wheels and some 255/40-17 track tires, and go have fun. You know they're quick - I seem to recall running down a certain silver Miata earlier this month at MSR, and we were both on the same tires.
Yes, mine has had it's share of issues (although every single one of them has been covered under warranty), but Jon's by comparison has 70k miles and hasn't had a single problem, so they're not all as fragile as mine.