They gotta pay more, and offer more bennies - even if the job is part time - because of exactly that. Part time or not...the compensation is not enough. We've lost drivers here and there every year I've been there that leave to go drive OTR because of total compensation.
They gotta get butts in the door applying. How do they do that? By making the job more attractive financially.
Or they create jobs that combine a couple different positions and boost pay. Bus Driver/Food Service, Bus Driver/IA, Bus Driver/Day Custodian.
Part of the issue is the idea that each of these jobs should be the equivalent of FT compensation.