OP: You do know that the stock exhaust manifold has the primary CAT built into it, right? If you're replacing the "front CAT," you just buy a new exhaust manifold and you're done. No where NEAR 800$....around 350% on RockAuto:
We have a secondary CAT after the rear O2 sensor, so it's more of a resonator than a CAT (because nothing is monitored after it). Is the car stock? Are you trying to do something custom for some reason?