All the buses I looked at before recently buying mine, the rear door was 36-38 inches wide. The narrowest wheelchair lift on the market today requires a 40' wide door. Quite frustrating
I ended up buying a 1982 Carpenter that had a lift at one time, so there is a 42' hatch behind the regular entry door, which was welded up when the lift was removed. So, I'm having to grind out those welds, and hopefully fashion a door from the metal plate, instead of buying a door.
So, yeah...buy one with a lift already in, or that has had one. Lifts are cheap ($300-500 used, all day long). If you can do the install, you can save a ton of money over buying a new lift and having it installed ($3000+).