When they throw back a counter offer it means they weren't completely disgusted with your offer. I bet if you let them stew on it for a little bit they will come down further, maybe not quite to your offer but I would be willing to bet $13K should be pretty easy for them to hit. Then its just a matter of if the price is right for you.
By the way, just so you are aware, these cars have a recommended 7500 mile oil change schedule (the car will adjust its flexible service monitor so you may even get more miles between services). For me that will probably be 2 years worth of driving, so the expensive oil change once in a blue moon doesn't bother me one way or the other. Just some more knowledge to pass on to you.