Damn 17-18K with any mileage is way too high! I bought my wife an 04 GT brand new for 20,000 out the door. Cars are worth what someone is willing to pay. But KBB.com is one of many good references to go by if your not sure what the car is worth. Unless this car is in awsome condition and its everything you want in a mustang you shouldn't pay more than 10,000. Let us know how it turns out...