Thanks for all your help everyone.
In the end I went with a full-size schoolbus instead of the shorty. I decided that traveling in my little station wagon is good enough, and I want the skoolie to be parked as a full-time residence.
To anyone else getting started and reading this, I second Seroflorus' comment about going to the local school system bus garage. I ended up buying my 1988 Chevrolet here in NC, and I was able to go and talk to the mechanic who had been working on it for more than a decade. He was super helpful and super nice and pointed me straight towards the bus that was in the best condition. They even provided me service records back to 2005.
Here in North Carolina they list all the county school buses for sale on a single website:
Those are state-owned school buses. Each county owns their own activity buses, which aren't listed online, you just have to call.