That P0420 code on a 2009 Subaru at 214k is almost never the sensors, it's the cat itself wearing out. Cleaned sensors might buy you a few weeks but the code will come back once the ECU runs its full readiness test cycle, usually around 50 to 100 miles of mixed driving. I went through this exact thing on my 2007 Forester and the light stayed off for nine days before popping back on during a highway run. You're not really fixing anything by wiping the code, you're just resetting the timer on a part that's already past its life. The $1,150 quote sounds about right for OEM but you can get an aftermarket cat for way less if money is tight. I'd keep that $28 receipt handy because you'll probably be back at that same AutoZone soon.

Bringing a small towel to wipe the lens between shots saved my salt spray shots last summer.

Did you know this same thing happens with tons of secondhand stuff people buy online? Like bikes where the guy never tightens the stem bolts, or treadmills that still have the shipping screws in the deck, and folks just assume extra hardware means it's supposed to be there. It's a weird mental block where people trust the machine more than the manual, so they skip the boring setup steps and pay for it later. I've learned to always ask for the manual when I buy used, even if it's just a PDF, because guessing costs way more than reading.