The bottom line is that the dealer wants to sell you a car, he doesn't want to see you walk out the door. So once you have all the information you think you can handle, go home and think about that and any other possible things that might come up then go back to the dealer with your list. Write the list down it doesn't matter but sit the guy down and give him your list of demands or ad ons and see what he says.
His first line will usually be "Wow you have thought this out" which then goes to "lets see what we can do" as he gets out his price book. With book in hand he will go through the prices your demands will add, he may even show you his prices so that he can convince you that he's doing everything on the very bottom dollar.
Once it's all added up he will give you a price which you naturally looked shocked at, then he will come up with a new price, he might do this several times dropping the price and talking to the dealer principle. After a little while he will give you a price and say "this is the best I can do, the boss is not going to like it but I can see you are serious and I want to see you drive away in a new car."
At this point if you are happy you sign the deal, however if you aren't happy and you think you deserve more you thank the guy for his time and walk straight for the door. Once the guy sees your back heading away from him he knows he's lost the sale so if you make it to the door without him calling you back, he's not prepared to go any better. The second he calls you back the ball is back in your court and he's bargaining again, you might not get everything you want which is where compromise comes in but you will soon find out if your deal is unreasonable.
If you don't get called back find another dealer and reassess your ideas. it's obviously not worth going to 20 dealers but you'll be suprised how much difference you can make going to 3 or 4 with the right information. It's also not a bad idea to make your first dealer one that you might not wish to deal with and use him as a test case to see how silly your demands are rather than annoy the guy you want to deal with with the trivial arguments because you can always take even the best quote from one dealer to another dealer and ask them to beat it.
Also remember that the new car salesman doesn't give a rats what the ad on parts cost they don't come out of his budget, sure he has to account for them in the cost of the car but the mark up has already covered that anyway so all he cares about is selling you a car with or without ad ons but the ad ons are where you bargaining power is.
