If you don't much about engines then what does it matter rotary or not? If you blow anything internal piston-wise or rotary you're going to be just as fucked.

Anyhow....you're numbers dont really make sense. You have an 18k limit, yet you want a GTO to eventually s/c (even though by the time it's paid off you'll have too many miles or other problems to want to mod it). But that's just you saying what you WANT, not really what you can get.

Anyway, I'd go VW. 1.8t or a rabbit. Or if you really dont care too much about performance and still like some downlow getup a TDI.