For standard replacement, I'd go for the $200 at the bottom of the RockAuto options. On a regularly driven car, these usually take care of the issue.
If you go for a performance downpipe like ZZP's, you may need to get the O2 codes turned off to avoid the high flow cat from setting it occasionally, and a harness extension for the harness to reach the different sensor placement. It's a better piece, but the extras will need to be considered, because the cat is less effective than a regular one, on purpose.
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