Looking for new car, would prefer something cheap/easily tunable

I'm in the market for a new car (I currently drive a Mitsubishi Raider), and am looking for something that is, bottom line, fun.
My budget is about 5k cash, 10k financing (if I go through a dealership).

Nothing is set in stone, but my preference rolls on both ends of the spectrum.
Ideally, I'd like a sleeper car, I've looked at Sentra SERs a lot, a Mazdaspeed 6, and a Volvo S60 R, but I'm not opposed to something sportier in styling like an S2000, Miata, or 350Z.

What are some good recommendations? I should mention that if it is a convertible I'd prefer a hardtop conversion (I haven't been able to find one for any mustangs)

thanks in advance, sorry if this is the wrong forum for this post.

Miata--
https://www.flyinmiata.com/V8/

I personally would go for an Accord myself. I have a friend that owned one for 20 years - >300k. The new Civic is awesome also.