Update. The dark blue bus mentioned above was gorgeous, we saw it Sunday. Looked brand new, no rust and mileage and engine hours made sense. Problem was it's a hair under 25ft long from bumper to bumper and the wheel wells would have put our bathroom to far forwards. If anyone wants this bus send me a message it'll do someone very well.
Our floorplan requires minimum of 29 feet, with 30-31ft being ideal.
So back to the rusty yellow bus above. It's the length, engine, ceiling height, and transmission that we want. And it's price is much better than the blue bus. But it's obviously got rust.
Besides the obvious answer of "none", how much rust is acceptable on a 2002 bus. Would anyone even consider trying to salvage this? Here's pics of the frame underside.IMG_20200511_132432_01.jpgIMG_20200511_132429_01.jpg