NGTD got most of it. The power of the wrx is only a head ache for a rally cross car. Out here I'm struggling to keep up with the non turbo cars both a cgi and a gd chassis. My 06 wrx has been reliable for the 90k-122k I've owned it and that inlcludes many autox and rallyx. If I was in your situation I'd find a 2.2 impress or a gc 2.5rs if you could afford it. I'm in so cal so I can't comment on rust.
E36 BMW. You might be able to find an ugly m3 around $5k if you look long enough.
One that looks like it's been rallycrossed? 
I guess i've autocrossed in both miatas and GC imprezas. If i was to pick a dual purpose car for rallycross too i would definitely pick the impreza. An n/a 5spd awd GC impreza is a really great all around car. They even handle decently out of the box. They are pretty easy to work on and there is a huge aftermarket. They even get about the same MPG as Miatas, too. My friend had a 2.2/auto/awd and was averaging 27mpg. The rear seats are very usable, even in the coupe, and they have a 'real' trunk.
I'm a repeat neon owner although ive never raced any of them, but the race potential is pretty obvious. They're faster than either an n/a miata or n/a GC, and it's fairly easy to make them handle. The sohc engine in particular is pretty dang reliable and easy to get another 15-20hp out of. They're pretty durable, pretty easy to work on, and pretty cheap to patch up when you break it.
You'll need to log in to post.
