Each stabilization and marketing plan may further provide for maximum charges for plant processing and transportation service on the market milk or market milk components which are transported to the area where sold. The stabilization and marketing plan may enumerate the applicable maximum charges, and may establish individual charges for each function enumerated. In establishing any such maximum charges for such transportation services, the director shall base such maximum charges upon the rates which are charged for actual or reasonably similar services by highway carriers, as the term “highway carriers” is defined in Secton 3511 of the Public Utilities Code.