Payment by the county to the office of the district attorney for the costs and necessary expenses of investigation, prosecution or defense of any action, actual or contemplated on behalf of said county, called for by Section 215.4 of Title 19 of the Oklahoma Statutes, shall be made upon certification of the amount of such expense by the district attorney by the filing of a regular purchase order with the county commissioners for payment out of their account for general government operation, or other account, as may be appropriate. Such claim shall be approved and paid forthwith whether or not encumbered in advance. An audit as to procedure and accounting of the process shall be made by the State Auditor and Inspector as a part of the regular county audit, the costs of which shall be part of the costs of regular county audit performed by such office.