Wild Pig looks like an exchange program, I may be wrong. The guy on ebay doesn't do an exchange program. You buy new headers with the CAT removed and then see your old ones.
They charge $150, and you are right, you get your $50 back when you return the stock pipe. My work blocked the ebay site so I could not see the price you were referencing.
I've got a stock head pipe with the cat removed,it's got abou 3500 miles on it I will sell for $125.00 plus $25.00 shipping the reason I'm selling is I'm going to a 2 in 1 exhaust. This pipe is off a 2011 sg. Pm me if interested