the 2000-2004 models of BMW M3s have mpg's in the 20's. try looking into those. they're sporty

I have a 06 350z 6 speed I get about 18-20 In town I live in a small town. Travailing An hour or more I can get 24-28. Very fun car.

I don't think you will find a Nissan skyline for $10k also all the cars you listed are in the low 20s for gas mileage and even lower. Performance and gas mileage don't mix well.

-Nissan 350z - Fast, spacious, little fun car. Gets decently good gas mileage for a sports car. They sound awesome starting up and reving
-Audi TT - Very small, small amount of room, don't even consider letting anyone ride in the back seat, fast but not as fast as the 350z. Look really good I must admit
-Mazda RX-8 - One of the worst options here IMO. They are known for the problems with the engine, it flooding or anything else. I would not get it personally with all the problems and money it will cost you. They do sound good but just not worth it.
-Chrysler Crossfire - Also nice looking car but doesn't compete with the 350z or TT. Very nice looking car though, nice interior
-Infiniti G35 - This is the most spacious out of all of them, it does weight the most and will take a little bit to get up to high speeds (not too long lol it's still a sports car) I do like the look of them but it's just to large to be a sports car IMO. It's a good choice right behind the 350z and TT.

Maybe go for an older Skyline.

R4TTY wrote

AMF wrote Maybe go for an older Skyline.

Very true but still nissan looks better

A Skyline is a Nissan... You won't be getting a older skyline for 10k either,

Should add a Subaru to that list ;)

I would say the best on the 350z or the RX-8.

The new versions of the RX-8 have gotten alot better on the mechanical issues. The only problem when you try and modify the rotary engine you have to throw out everything you think you may know about doing so. The whole game plan is different, But they can be monsters if they are done right!

The 350z also can be pretty quick for reasonably cheap. Twin turbo they can become monsters on the street. My step brother has one and he LOVES it, and its pretty quick.

IMO I would say the rx-8, I've gotten to drive one and they are pretty well rounded cars. The one i drove shot flames and was decently fast too. Good Luck!

G35 if you need the back seats. It's not that much slower than the 350z and looks sporty. E46 M3 or 335is would be good too, if you can find one in good condition