If the bus is in good enough shape and has little rust,
Buy it do what you need for awhile, forget rebuilding the gasser, find a 5.9 Cummins to drop in and go.
The gasser just need to run good enough to get you home by the sound of it.
I find running 5.9 12 valve Cummins for $1000 all day around here.
A junkyard repower could be done for as little as $1500.
It all depends on what you have at your disposal for tools and other resources.
"Don't argue with stupid people. They will just drag you down to their level, and beat you up with experience."
Patently waiting for the apocalypses to level the playing field in this physiological game of life commonly known as Civilization