I did this for my mother once when she wanted to buy a car with cash. There are several books around that will help you accurately estimate the amount the dealer has in a car. I don't remember which but it should be easy to find. Anyway, once I figured out how much the dealer (Jerry Damson Honda in Huntsville) had in the car I went to their lot. Of course one of their salesmen was on me immediately and I sat down with him in his office. I pulled out my calculations and I told him that I believed he had $X invested in the car I wanted. I then told him that if he would take $X + $200 he would have a quick sale and I'd be out of his hair in 5 minutes. Also, that if that didn't seem like a good deal to him I would be on my way. He took that deal and I was gone off the lot in 20 minutes