In Etowah County, in addition to the compensation paid any returning officer, the county governing body shall supplement the mileage allowance, already provided for by the general law for each such officer, to pay each a total of fifteen cents ($0.15) per mile in going to the courthouse and returning to the place of holding the election. Such supplement shall be paid from funds out of the county treasury not otherwise appropriated. Provided, however, in the case of municipal elections within the county, such supplements for returning officers shall be paid out of municipal funds, not otherwise appropriated, by the municipal governing body.