go to a credit union and get approval based on the type of car and price you’re looking at. then compare that to whatever they tell you at the dealer. Don’t tell them the credit union part up front, wait until their finance offer sucks then show them and have them beat it if they can.
as for the price of the car once you find the one you want:
don’t talk payments, only the full price of the car… tell them you’re not financing until you get them as low as possible on the price, then ask them about financing, otherwise they’ll screw you at the other end of the deal to make their money.
it’s a little like playing poker, don’t show your cards until it’s in your favor if possible.