Cars.com and autotrader.com are normally pretty close to what they price cars at, I have a very good friend that owns the Ford dealership here locally, so getting cost is not a problem, when you start pushing to cut into the dealer hold backs, you are pushing the limits of what many dealers will do, the low cost leaders you see all year long, some below factory invoice are already cutting into those hold backs. As far as financing, make sure and check with your local banks, or if you are a member of a credit union in good standing, see what they will give you a loan for, I got a personal loan to buy my 5th wheel and the interest is at 1.75% I told them how much I needed and went and picked a check up made out to the person I bought the trailer from. One other thing to take into account, check your insurance rates on the vehicle you are looking at, also check with your insurance company, many of them these days are offering pretty good financing if you have your insurance with them. Some of the credit card companies also have programs for auto purchases, I know my Citi, Discover and my Costco card offers car deals with good financing. Make sure and check all avenues.
And remember, you are going to loose money on a new car purchase as RBH said, sometimes is really pays to look at dealer demos or used new cars that were sold and then traded back in often times you will get far more car with options at quite a discount, if it is your first new car, then throw that out the window, but remember it can save you a lot of money to look at a slightly used car. Again, as RBH stated, many of the little things we think we need or we know we need can be purchase much less expensive at after market places, I know our local Rhino Liner Dealer will undercoat any car or truck on the market for about $150.00, which is far less expensive than any of the dealers will.
One other thing to remember, dealers rarely own those vehicle that they have on the lot, they pay flooring(interest) every single month on those cars, some of them if they sit on them for a while, they actually end up loosing money of them, no matter how much they sell them for, often times the only money they make on cars is the year end hold backs they get from the manufactures, which these days is pretty small. Also, they have to pay a part of the advertising that you see the manufactures doing, IE: If Toyota is running and ad and you see your local dealers name at the end of the piece, it means they paid a co-op fee to the manufacture for that ad. I am not saying don't negotiate for the best deal you can get, but also don't be so stubborn, you don't let them make any money, they got to make something somewhere or they are no longer in business. Also be willing to patronize their service facilities if they meet your expectations, when you are talking to the salesman, make sure and have him introduce you to the Service Manager and Parts Manager, look at the shop, see how they do business, if they get to know you, it goes a long ways to having a great relationship and they do want you to come back.