Check out
truecar.com. They'll show you the prices that people are actually paying for 370 Z's in your area. You can configure it with options and get an idea of MSRP vs invoice vs market prices.
It's just another tool in your negotiating toolbox, but I and a few friends have found their numbers to be generally pretty good. You may be able to do better, but it's a start and gives you an idea of where you "should" be. If nothing else, the "Certified Dealer" numbers you give you something you can print & take to your salesman, "beat this". I've had a couple of salesmen gripe at me about using Truecar numbers from other dealerships, which I take as a good sign.
FYI...
2013 370Z Touring + Sport + SatNav + Kick plates = $43,990 MSRP. Invoice = $40,857. TrueCar has "certified dealers" that say they'll do the deal for $39,154 (in my area).
Good luck!