Where (and when) it stops nobody knows.
Filters!
Just picked up a Wix air filter at O'Reilly, 26 bucks and change.
They had two cabin filters, one was a Wix and the other was their store brand, Microguard, 23 and 22 bucks, respectively. Seemed like a lot. The OEM is about 25.00
So, I checked Amazon and just ordered a Bosch engine air filter and an "EPAuto" cabin filter, for a total of just under 28 bucks. I think these will work just fine for a year.
I've purchased more Bosch filters in my lifetime than I can count.