Check NADA for comparable cars (enter same mileage too) to determine market value depreciation. That should be a fair target for the amount LESS you pay for the '10 vs. the '11 model. I don't think dealers pay taxes on the cars they haven't sold (probably varies by state) but they are paying insurance and have lost money advertising the car, washing it, fuel for any test drives, etc. Most people think the best way to get a deal on a car is to buy one that's been sitting for a long time, but actually it's best to take one the moment it's being pulled off a truck. Then it doesn't really cost the dealer anything except some basic prep. Inventory has carrying costs for any business but it can also be a tax deduction.
In reality you should be able to get a killer deal on it. I just picked up a new 2009 "leftover" sportbike for $3k under the MSRP. It all depends how hard you negotiate and what you're willing to spend. For a leftover in-stock vehicle cash is king and if you're serious the dealer should be too. If you have a firm # in your head bring out your wallet and ask to speak with the sales manager. Offer him what you're willing to pay bottom line and be serious about it.
If they don't accept it you can always write a check for the car in full (note that on the check) but don't sign it. Walk out and tell them to call you when the car is ready for you at that price.
