Some nissan cars are pretty reliable (mostly the newer ones). My 06 Xterra is pretty much bullet proof.
If I HAD to choose between a mustang and a c4 vette, I would probably go with the C4. I've always liked the Grand Sport vette's. I know the Grand sport's are WAY out of your price range, but if you get a C4 with a LT1, and buy edelbrock's LT4 conversion kit you will have enough power to run with newer vettes.
edelbrock kit
http://www.jegs.com/i/Edelbrock/350/7109K/10002/-1
While you're at it, you might as well throw in an eagle stroker kit
http://www.jegs.com/i/Eagle/356/B13004L/10002/-1
Add a few bolt-ons, such as a larger throttle body, injectors, intake, headers, catback, and a good tune and you should be pushing close to 500hp (edelbrock claims over 400hp with just the top end kit.)
Or you could just leave it mostly stock (add a few bolt ons) and still have a quick car.
Try getting that much power out of a 99-04 mustang GT without adding forced induction.