The only time you should enter a dealership is to test drive the car or sign the paper work.
Send an email to every dealer in your area that has the car you want (most have their inventory online). Tell them you want the drive out price, tags, taxes - EVERYTHING on a specific car or if they don't have an online inventory, tell them what you want and tell them you want the drive out price info to include the model, color and options. Pick the best price for the car you want.
Then go to your bank and take out a loan for that amount of money and get a sight draft to take to the dealer.
IF the dealer can offer you a better loan, then check it out but do this independently on the price you pay for the car.
Don't get addons like rust or weather proofing. If you're borrowing more than 80% of the value of the car, it's best to get Gap Insurance. If there's interest on the car, pay for this separately.
And don't trade a car in - sell it on your own
Car salesman are there to sell you a car at the highest possible price. They are not your friend and if you end up with a car you can't afford, they couldn't care less. But they are business people and if you're serious about buying a car, get the price before you walk in and if they try to change it, walk back out again