Rates for the rental of equipment owned by the fund shall be set to cover all costs of maintenance and repair, material and supplies consumed in operating or maintaining the equipment, and the future replacement thereof. The rates shall be determined by the county engineer or other appointee of the county legislative body and shall be subject to annual review by the legislative body. This section does not restrict the ability of the county road administration board to directly inquire into the process of setting rental rates while performing its statutory oversight responsibility.