Here in Australia, most schools don't own their own buses (I see a few expensive private schools do). Buses are provided by private bus companies and/or by a government-owned bus company (depending on who provides regular non-school bus services in the area). The bus fare is either paid by the student's parents, or else by the government, depending on factors like how long it would take the student to walk, how old the student is, whether they have a disability, etc. The government subsidises buses for all school students equally, irrespective of whether they attend private schools or government-run schools. I don't know how exactly schools decide their start times, but I doubt bus availability would have much to do with it. Bus availability is something for bus companies to worry about, not schools.