Is ~$300 really expensive for a ceramic DC 4-2-1? I don't think so myself. Works just fine on our race car and has NO rust on it at all. The only time you will see rust is where the coating has come off-which it should not. As for power gains-ONLY a dyno will tell you for sure.
Where to buy-try Ultra Performance in Tucson or Summit. You might be surprised at the prices they offer.