Paul i hate to tell but any cat under $100 probably wouldn't help you pass any E-test a cat is worth $100 in scrap metal( due to the precious metals inside that actually due the work). I have installed many cats that people brought in to replace there OEM one that sometimes made emission results worst then the first time. And most cheap cats on newer OBDII systems will be setting P0420 codes all the time.

If you go to a repair shop and have your vehicle diagnosed and they say it needs a cat. Most likely they are not going to be able to repair it for under $450. so then get you a conditional pass. So it might cost you $100 which is what you spend on 4 e-test if your didn't pass 4 times.