Get something cheap and easy to maintain. Cars are a horrible investment, as you never get as much out of them as you paid, unless you get an awesome deal to begin with. I paid $2200 for my 240sx, and its a great car. Sure it has some body work that needs to be done... but considering I got it a year and a half ago and it runs fantastic... I couldn't be happier. You're 18, no need to burden yourself with the weight of a car payment.
Get an Altima, Maxima, Camry, Civic, Accord, etc.
Don't get any kind of sports car. They get you in trouble, and they're just not practical. You have the rest of your life to get your dream car.
Nissan 300zx TT
Lexus SC300
Prelude SH
Nissan 240
All coupes and available in a manual transmission. Can also be had for the budget you are working with .
300ZX TT = NO way in hell. Expensive to maintain, extremely difficult to work on.
SC300 = Decent car. Being a Lexus it is again very expensive to maintain.
Prelude = Excellent cars. I would recommend this to a college student.
240sx = I love these cars. Easy as pie to work on and maintain. Cheap to maintain. A blast to drive. I've owned them since before I had a license.