Whenever the commissioner finds it necessary or advisable to make an extra examination of a credit union, the commissioner may charge the credit union a fee for the examination. In determining the fee, the commissioner may use the estimated average hourly cost, including, but not limited to, overhead, for each examiner engaged in the extra examination, and the credit union shall, within 10 days after the mailing or other delivery of a statement by the commissioner, pay the fee charged by the commissioner.