In addition to any maintenance tax imposed under section 242.490, the board of supervisors may set an annual processing fee for assessed tracts when the board determines that the costs of preparation and processing of the district’s maintenance tax statement for such tracts exceed the amount of tax imposed. The amount of the fee shall be determined by the board of supervisors at the meeting in which the board sets the maintenance tax under section 242.490. Such fee shall be used solely to reimburse the district for the costs associated with processing annual maintenance statements.