In suburban Chicagoland it costs about $5 to provide a ride on a bus for normal passengers. The agency has a goal of recovering half of the operating cost from the fare, leaving the rest to come from government subsidy. Some lines gain opering fares by contracting with private employers to meet their employees particular needs, this can even reduce the cost to zero for those employees as a benefit.
The goverment role provides two primary benefits. One is to reduce traffic congestion, and consequently reduce road maintainance and improvement costs. The other is to provide mobility to members of the public without access to a car.
ive read that in boston the goal is to keep the cost of each route to $3.30 per passenter or lower.
if the average cost creeps above that benchmark the route is usually discontinued or combined with an other one.
on a side note, the average cost per passenger for the 'night owl' service that boston provided a few years back was nearly $10. however, they still charged the standard fare.