it was decided that they were not allowed on our district property. So we had to pay tuition and transportation costs to a neighboring district.

You've given the only answer that matters to the OP's question, and frankly the rest of the thread doesn't even need to be here.

Kids don't get expelled because the schools still have to provide them an education one way or another, and every option besides leaving them in the regular school is more expensive. Alternative schools, self-contained small groups with extra teachers. Bussing to another district. Whatever the alternative is that's offered, it costs more than just having them be one of 40 students in the standard classrooms, so districts have largely gotten rid of all the other options.

I guarantee that the minute a district comes up with some kind of alternative placement option that's cheaper per-student than normal school, 95% of the excuses not to expel will disappear overnight.