§ 719. Expenses. If a public defender serves more than one county, the expenses of salaries, maintenance and operation of his office shall be shared by the participating counties in accordance with the provisions of the agreement establishing the office. Expenses incidental to individual cases shall be paid by the county for which the services were rendered. All expenses chargeable to a county hereunder shall be a county charge to be paid upon certification by the county treasurer out of an appropriation made for such purposes.