I would be very cautious about purchasing a bus from AZ with those kinds of miles. Historically AZ has had pretty good buses. But over the last 5-10 years they have had some major funding issues requiring them to keep buses considerably longer than they have in the past.
It also means they haven't spent the $$$ necessary to keep everything running well. It hasn't been that long ago that an AZ BB AA RE bus left the rear end of the bus as it went down the street. There has to be some very serious maintenance and driver daily inspection lapses that would allow a rear end to drop off.
In most calculations school bus duty is only second to garbage truck service for severe duty. It isn't that when they are running that they work that hard. It is the number of on/off cycles that kill them. It also doesn't help that the short duration of each cycle can mean the engine does not get up to proper operating temperatures. This sort of duty cycle exacerbates the issues in regards to emissions equipment since most of them rely on hot engines to make them work properly. Short answer, for every school bus mile it is considered to be 2x of normal service duty miles.
A BB of that age would be a low roof if the inside of the windows have two buttons and a high roof would have three buttons holding the windows to the window posts. Outside you can visually see the difference between 9" and 12" windows by where the top line of the windows are in relation to the driver's side window and the top of the service door. 9" equals the top of the driver's side window and the top of the service door and 12" line up above them.
Unless you can figure out if any major work has been done to the bus I would not pay more than $3.5K for a bus of that age with those kinds of miles, particularly one with the MT643 transmission.
