The director shall establish a separate account for each marketing plan established under the provisions of this chapter, and all license fees and assessments collected under any such marketing plan shall be deposited in its separate account to be used only for the purpose of carrying out the provisions of such marketing plan: PROVIDED, That the director may deduct from each such account the necessary costs incurred by the department. Such costs shall be prorated among the several marketing plans if more than one is in existence under the provisions of this chapter.