I've got no cat and Charles @ Mainstream built my exhaust custom. Cat's vary greatly in price depending on the amount of precious metals in them. Gold and Platinum are what make Catalytic converters work, when they heat up to a certain temperature the metal(gold/platinum) has a chemical reaction that bonds the Carbon Monoxide and other polluting byproducts of the engine. Make sure that you get a cat that has the least amount of cells/square inch. Catco makes a decent one. I know that Apexi makes one that flows as if there is no cat, it costs about $1200. Most of the Japanese time attack and JGTC cars run them. On a full out race car they produce 0 ppm of Carbon monoxide. lol, they are good but I don't think you want to spend that much.