A holder of a certificate A, B, or C with less than twenty vehicles must semiannually on or before January first and July first of each year pay to the Office of Regulatory Staff the following fees: for vehicles weighing not more than two thousand pounds, seven dollars and fifty cents; and for vehicles weighing in excess of two thousand pounds, seven dollars and fifty cents for the first two thousand pounds and two dollars and fifty cents additional for each additional five hundred pounds or part thereof of weight, except that the total license fee may not exceed fifty dollars per vehicle semiannually.