The proration zone agent for each marketing program shall collect, either for each primary certificate or for each secondary certificate, or for both, a reasonable and proportional fee to be fixed by the program committee, subject to the approval of the director, so calculated as to provide an amount which is adequate to defray the necessary expenses of instituting and carrying out the marketing program and a proper proportion of the cost of the maintenance of the department in the performance of duties which are required by this chapter.