Have you considered looking at the Colorado buses? I'm guessing short bus for maneuverability, maybe a hill climber for boondocking?
There's definitely short buses for under $5k in the west. It just depends on how new and what condition you want to start with. Public Surplus seems to have overall the best prices, but it's a buyer beware situation. If you're not mechanically inclined you can still look at the buses in the sale and may have an opportunity to talk to the mechanics. They'll usually tell you what they know.
Beyond that there's GovLiquidation who sometimes has buses. Most of the buses on Craigslist have have simply been bought from Public Surplus and had the purchase price doubled, but not always.
You need to know what you're specifically looking for, rather than just a short bus body. Diesel vs gas, hill climber vs highway, stick or automatic? A weekender or a live in?
You're about to inundated with advice from multiple sources. Get ready.