You're looking for cheap pads, which is an awful idea BTW, but you're also looking for ceramic pads? If you're not a "car guy", don't just pick up random parts because you've heard people talking about them. Ceramic pads are extremely noisy in street conditions and they will chew the *sugar* out of your rotors. Plus they're usually more expensive.
Complaining about markup on pads for the Model 3 is a bit funny, too. You've bought an expensive car, the replacement parts are going to be expensive too. If you want upgraded parts, they'll be even more expensive.
brake pads, aftermarket, a lot.