The advisory board which is appointed by the director to assist him in administering each marketing order shall recommend to the director, from time to time, budgets to cover necessary expenses, and budgets to cover the expenses of carrying out sales promotion plans if such plans are authorized in the marketing order, and the assessment rates which are necessary to provide sufficient funds. If the director finds that each such budget and assessment rate are proper and equitable and will provide sufficient moneys to defray the expenses which may be incurred, he may approve such budget and rate of assessment and order that each producer and handler so assessed shall pay to the director, at such times and in such installments as the director may prescribe, an assessment which is based upon the units in which such commodity is marketed, or upon any other uniform basis which the director determines to be reasonable and equitable.