Before making any purchase for supplies, materials, equipment, opportunity shall be given for competition, under such rules and regulations, and with such exceptions, as the board of commissioners may prescribe by ordinance. All expenditures for supplies, materials, equipment, involving more than two thousand dollars shall be made on a written contract, and such contract shall be awarded to the lowest responsible bidder after such public notice and competition as may be prescribed by ordinance and not in conflict with the General Law of the state.
(Charter 1989, Sec. 25.)