The commissioner may make special examinations or render special services to banks, either at the request of banks desiring same, or at his own instance. The commissioner shall have discretion to decide whether any examinations or services are sufficiently urgent, out of routine, or extraordinary to be denominated special examinations or services. When any special examination or services are rendered and so denominated by the commissioner he shall charge the bank so examined or served the cost based on the average daily cost of all examiners of the department plus actual and necessary expenses. The bank so receiving such special examination or services shall pay the per diem and expenses of each appointed examiner performing the work to the commissioner, who in turn will pay the amount into the department maintenance fund and disburse to the examiner directly the amount of his services. An examiner who is on the state payroll may perform such services but the funds so derived from his services shall be paid into the department maintenance fund, and no examiner shall be allowed to draw from a salary and expenses from both the bank and the state.