you can study for the written part, but for the driving part you would have to have an approved trainer to teach you to drive. after I retired, I drove a school bus for a few years but the county transportation dept was licensed to teach the driving part.
I had a class-B which was good for school busses, dumptrucks, etc.
plus for a school bus I had to have two different endorsments, passenger and school bus.
the passenger endorsement would allow you to drive a small bus like an old folks home would have.
I can't tell you the cost of all that, but a lot of people would hire on with the county as a school-bus driver and when they got their license they would quit and drive a dump truck.