A good condition 951 in need of some DIY wrenching- maybe one with a bad clutch that is otherwise nice.. can be had for 5K$.
Or a 914 already set up like this one
http://forums.pelicanparts.com/porsche-cars-sale/500489-feeler-1973-914-sale.html
As far as non-Porsches go... I always thought it'd be cool to have a olive drab YJ jeep, no doors, just to bomb around in.