Here is my experience from last year with buying a new GM car:
I was in the market for a new car and was just browsing. I started off at my local no hassle dealership. Every car has the price on the windshield. It's the price period. No barginning, no padding costs, nothing but the price. The cost in the case you're talking about would have been $18,500 for the car I bought. Then you'd either subtract the $4,500 or the $1,500 depending on which incentive you took. I also got a $1,000 incentive for owing a GM car. So when all was said and done I got the new car for $13,000 a darn good deal. They were very straightforward about the pricing, very easy to deal with and overall a pleasurable experience.
Now to contrast this. That same day before I bought my car I went to a different dealership to compare prices before I commited myself to the first deal. These guys were slime. They kept saying how they'd match any deal I had previously gotten. Not only that but since they didn't have any 2003s that matched the other dealerships car they would do it in a 2004. They asked me how much I was going to pay and I told them $13,000. THey asked me how much I was going to put down, I told them $4,000. After spending about 1 1/2 hours finding a car, having the salesman talk to his boss, filling out some preliminary paperwork and such they we so happy to be able to match the $13,000 price. It was pretty easy. They started with $22,500, subtracted $4,500 and $1,000 for the rebates then subsracted my $4,000 downpayment and got $13,000. After all of that I had to explain to these idiots that the $13,000 was the price of the other car, not the price after I put down $4,000. So after working this hard to get the price to $17,000 and acting like they were losing money onthe deal they "reworked" the numbers again and managed to get it as low as $15,000. After spending 2 hours in that place they were still $2,000 higher and they couldn't understand why I wasn't buying thier car.
I'm sorry to have gone on for so long. I guess what I'm really trying to say is find a good honest dealer and buy from them. Some dealers will "juggle" the numbers making it look like you've got a good deal when you really don't. Just compare the final price to you when deciding who you will be buying from.