if you go with a 70s MB SL, the 380 engine had a tendency to have problems with the engine timing chain. Many of them have been upgraded by now, but good to ask about it. Also, if you go very old (1974), you can find them with manual tranny.
I agree with a lot of what was said. Here are some others that I have heard are pretty easy to own.
bmw 318i
Saab 900
Mitsubishi 3000GT
Mitsubishi Eclipse
Subaru SVX
Alfa Romeo Alfetta GT / GTV (this one might be a little less reliable than the others)
if you want to go REALLY cheap
70s rabbit/golf - if you want sport, I would stay away from the 48 HP diesel one I had
Ford Escort GT - a friend of mine had one of these and it was a lot of fun
What is nice about the really cheap ones, it breaks down, leave it you take your plates and hitchhike home.