A high-performance car is a thrill to drive until the maintenance bill arrives. Replacing pads and rotors is a necessary evil that ensures you can actually stop, but it hits the wallet hard at once.
You will likely spend about $900 for a quality set. Prices for these parts rarely drop, so waiting for a sale is usually a waste of time. Focus your energy on finding a shop that will let you bring your own parts to save on labor markups.
The 0% intro APR is a deadline, not free money. If you have any balance left after the 15 months are up, you will start paying interest on the remaining amount.