Just remember the price of the car isn't the only thing you gotta worry about, LOTS of dealers would give you a price that sounds really good, but the trick/scam they use is in the APR and payment plan. As I've posted in another thread, the first sales person I spoke to offered me a GSR for $29xxx out door, an APR that's "Between 3 and 4%", and along with that a monthly payment. The payment sounded a bit high so I went home, after some research online I realized he was trying to charge me at a rate of 11%, the standard rate should be around 5-6% with decent credits, so that extra 5-6% will go into the dealer's pocket.
So when you are at the dealer, only negotiate the car price as if you are paying in cash, do NOT trust any APR or monthly payment numbers that the SALES PERSON gives you. I finally bought my car at a dealership which I only negotiated the price of the car with the salesman, I didn't even talk about the interest rate and payments until I sat down with the finance agent at the dealership, and he showed me the APR offered by all the available banks at the time (on his monitor), and worked out the payments from there.