It's really difficult to compare one sale to the next.
Unless both sales have no trade, the same sales tax, same title & license fees, and you don't use the dealer for financing (bring your own financing with you), those are all variables that change what you pay for the car, OTD.
For example, the salesman can afford to go much lower on the price of the car if he screws you out of $$$$ on your trade. They do similar deals on financing, but those are harder to spot unless you have shopped around and know your credit score.
I'm going through this now. I'm negotiating the price of the car (including state tax and other fees) apart from financing and trade. I have my own financing from Capital One (Blank Check, neat way to do it) and I'm not even going to talk about a trade until after price of the car is settled.
My best price so far for a MS3 GT, no options, no nav: $23,825.
Add state sales tax, title, license, registration, "document fees", and the best OTD price is $25,300.
I'm going through another round tomorrow and will try to get them down another $800-$1000. Hey dudes, if you're reading, first one to get me the car for $24,300 total OTD gets the sale. No questions asked.
The best tool is the mazdausa.com website. It shows you what the dealers have in stock, what color, down to the last option. I know there are 6 MS3GTs in the color I want in my area.
One salesperson told me she had the LAST MS3GT in my entire region. He currently has the lowest price, but I don't want to give my business to such a blatant liar.