Aftermarket cats generally don't pass emissions tests, beware of them if you really need to pass an emission test. Does NY use a real emissions sniffer or just use a scan tool to look at emission related PCM tests? My understanding is that most places now just use a scan tool to look at the PCMs self diagnostic tests, and if all the monitors (tests) pass, your car is emission compliant.
It actually might be cheapest and most effective to find some OEM cat from a low mileage junkyard vehicle and have it specially fitted to your exhaust, and then get the O2 sensors fitted. If you can find a place that won't rape you on prices, it should be far cheaper than an OEM replacement.
I sold my SVT cat with about 15K original miles for like $90. I feel completely retarded right now.