13K seems rather high to me. What year model is it? For that price, I would expect a bus that is less than 10 years old, with good tires, and with factory air conditioning.
Don't let "fleet maintained" sound like a perk. Few individuals buy a bus brand new from the factory, so they're all "fleet maintained". My bus was maintained by Montgomery County Public Schools in Maryland, and there is a lot of mismatched hardware.
Typically, school systems are in a rush to get them "fixed" and back on the road as fast and cheap as possible. They also aren't known for having the best pay scales.
Look around the forum, you'll see a lot of people get their bus for under 5K.
Good luck, and welcome!