98 civic PO420 check engine code

So, I'm stumped by this... My dad and I checked the code, and it was PO420, which is either a bad oxygen sensor (primary or secondary) or a leak in the catalytic converter/exhaust system, and we manually checked the o2 sensors and they were both excellent, and I don't know what to do... There aren't any exhaust leaks, but I don't want to take it into a shop, b/c they're way too overpriced... I even replaced the front o2 sensor b/c the guy at autozone said that was what was wrong... guess not.

your cat is gone ;)

lol nope, last time i checked it was still there... but yeah, i have no clue...

your catalytic converter is no good.