No mileage shall be payable to constables for travel in service of any process or papers in any action, or performance of any official duty, when traveling in state, county, or other publicly-owned vehicles; but a record of such mileage shall be kept for reporting and taxing as provided in § 8-21-1020; provided, further, that actual mileage at the current county rate per mile for travel by privately-owned vehicle, or actual cost of travel by common carrier, and subsistence as provided by law may be paid to constables traveling in performance of duty, but shall be paid from the general funds of the county on warrant of the magistrate (or clerk of the court) before which the case or proceeding is pending to the county treasurer.