Sounds like a decent deal. I bought my car a few months ago (almost identical to the one your looking at but with 95k miles and a manual). I paid 15k out the door. You shouldn't need an extended warranty. But then again I don't know whether you beat on your car or not. If possible, get a trusted mechanic of yours to take a look at the car before you buy it. Good luck.
Buying from a dealer you will always pay more. That car has low miles so that is a plus. If you really like the car, if it is the color, options etc, then you can feel better paying a little more than book value. If I were you, I would shoot for $15,500 OTD.