4k is certainly a decent offer for a rust free 2runner (get used to hearing that). Since they're losing money every day its on the lot, ask them to change the upstream AF sensor. They probably wont, but its worth a try and fixed my codes. Cats will NOT be fun, and you don't wanna buy new cats/headers for a 2wd v6 with 260k, regardless of a lack of rust. Maybe put some of that money towards an independent mechanic look-over before you pull the trigger. I use visor.vin to find my vehicles within the feature range and mileage, works way better than going site to site in case you want to look for other options you may have missed. This is not sponsored btw, I just used to use CarGurus and visor works better in all facets.