be careful on Ebay... alot of people sell "OEM Style" parts or "Weapon R Style" for example. Usually that means its not really the Weapon R, or OEM, but its in the "style" of them. Kind of like the ECU upgrade that guarantees 25+ HP for like $29.95
Just buy the name brand stuff. And think before you bid, if the price is too low.. chances are there's a reason for it. However, I was able to get a nice exhaust system (comptech) for only $400 + shipping.
You can definitely save a buck or two. Just be careful...