Yeah, I bought a truck with 53k miles on it for $9k and put $11k in the conversion (and a lot of sweat). For 20 grand I have been running Rojo all over the nation.
Besides, most school buses ride horrible. If you find one that is air ride, most of the time the front is still leaf springs. The gearing is set up for around town and you have to run them to death just to keep up on the highway. There are obviously exceptions out there, but I either go truck or tour bus. I have owned both. There are good and bad points depending on what you want. Anyhow, I have stayed away from school bus conversions on purpose........one man's opinion.