Hooray for someone knowing a budget and actually sticking to it (GTO anyone?).
My previous car (2000 Trans Am) was from Carmax. We found the price to be decent. It ended up having obviously been in a front-left collision as the paint was swirled and stuff in the engine bay welded/replaced. It was enough to pass Carmax's inspection but not enough to pass my inspection. So I traded it in for the p5 and walked out w/$1,300 in cash.
Wherever you go, take your time. Before you buy a used car, look over everything. My dad and I spent 2 hours messing with that T/A in the showroom. We never noticed the paint swirls since it was inside and I was too "zomg I can go fast in a straight line" to notice the repairs. But we messed with the T-Tops, the headlights, fog lights, turn signals, hazard lights, brake lights, parking brake, stereo, spare tire (we even took it out), various fluids, windows, cup holders, seat belts, etc. We did everything short of changing a wheel.
One suggestion - have a price in your mind that you're willing to pay for each month and then tell the dealer $50 less. If they won't even work with you, then you're wasting your time - best to go somewhere else.