I agree that a full box MH (Class A) would be the best starting point.
Seems they are proud of them up in ID.
Here's a 70's class C in your price range in Idaho
https://pullman.craigslist.org/rvs/6091052808.html
But if you can wait or spread the search area and find something like this
https://phoenix.craigslist.org/nph/rvs/6030638119.html
You would be better off.
Read up on the late 70s stuff (better brakes, suspension) and the wheels (Nick's garage had issues with 16 or 16.5? on his)