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Either the cat is bad and the O2 sensor is working properly or the other way around. Throw a bottle of CATACLEAN in the gas tank and see if the code goes away. If that doesn't work, you'll want to rule out the O2 sensors before replacing a cat. You can get NTK (OEM) on RockAuto for a good price, but they're still expensive, so don't just throw parts at the problem. Cats are even more expensive, so make sure it's bad before replacing it. Lots of youtube videos out there on how to diagnose O2 sensors and cats. Grab a multimeter and an infrared thermometer. You can also remove the primary O2 sensor, borrow a borescope from AutoZone, and inspect the cat's internals.

What's your mileage? Cats sometimes go bad with age but more often from damage caused by oil burning or running rich. If the cat truly is bad, you're gonna wanna figure out why because putting a new cat on a motor that's burning oil, for example, is an expensive, temporary fix. Without resolving the oil burning issue, the new cat is gonna go bad too. Hope that helps.