The price of the Pedal Commander is set by the manufacture not the individual dealers. Any discount must be approved by the manufacture. If you buy a used PC it will not be covered by the warranty, however you may be able to save some money on it. You can adjust the throttle response with a tuner, however it is not comparable to the response that you can achieve with the PC. You can run both a tuner and the PC at the same time and they do very well together, however I'd make sure you let your tuner know that you also have a PC. Pedal Commanders can be purchased from a couple of vendors here on the forum including Nick and Matt at Moe's Performance.
Jay