What did you think of the G5?
My dad thought I was a fool for buying a GTP, but I am enjoying. You should buy an econo-box with a stick and if you're going to throw parts at it, only throw handling parts in and enjoy the twisties and good fuel milage.
I'm closer to 30 than 20 and I only now can finally afford to put a little bit of money into a semi-fun car.
I'm with everybody else who says that at 17 you shouldn't get yourself too far behind in money. If you can afford to pay cash, buy that car, but take out a small loan on it and build some credit, when you get older and are ready to buy something bigger, you'll be happy that you did.