new honda cats are approximately $500.

however, by federal statute, i believe honda has to replace your cat for free if it breaks within 8 years of the car being purchased, as long as the cat's never been altered. they might give you trouble about that, but that's the law, IIRC. you can try taking it back to the dealer (i'd put your stock exhaust on just in case)

as far as OBD2 high flow cats go, stick to the better brands like carsound or random tech, and make sure they're obd2 compliant and they should be ok. if your car still throws a CEL, you can get an O2 sim to get rid of it.