Whenever two or more political subdivisions establish a district pursuant to § 63.2-306 there shall be appointed a district fiscal officer for such district board. The district fiscal officer shall perform all the fiscal functions for the district board that had been previously performed for the local board by the treasurer or other fiscal officer of each locality within the district. The district fiscal officer for such district board shall be the treasurer of one of the participating counties or cities or combination of counties and cities, as mutually agreed upon by the district board with the approval of the governing bodies. In the event the local authorities cannot agree on the selection of a district fiscal officer, the Commissioner shall designate such district fiscal officer. For his services as district fiscal officer, the treasurer shall be paid such salary as may be agreed upon by the district board. In the event the district board and the treasurer so designated cannot agree on such compensation, then the amount of salary to be paid shall be determined by a court of competent jurisdiction and the amount so fixed by the judge shall be binding upon both the treasurer and the district board. Provided, that nothing contained in this section shall affect the regular salary or expense allowance of the treasurer as fixed annually by the State Compensation Board.