comparatively cheap? compared to real high end diesels maybe, but 4,5,6 thou to rebuild ain't cheap for me .... and the cruise speed depends on the vehicle it's in and it's rear gears and trans, it's not a high RPM machine
what's to fix aside from an engine that may have half a million miles or more of abuse, might be the air bag suspension, rusty frame from sitting in that tall grass for years, any number of age related leaks and wear on doors and hatches, etc etc etc .... jhaa asked about the bus generally, not just the engine
Bill