Drive-ins have no less overhead. They require much more expensive D-Cinema projectors (for higher lumen output), more real estate, radio transmission equipment

Drive-ins have no less overhead. They require much more expensive D-Cinema projectors (for higher lumen output), more real estate, radio transmission equipment and all the same expenses as conventional theatres except potentially less manhours required to clean the 'auditoriums.' They are likely cheaper in your experience because drive-ins are almost exclusively independent and in rural areas.