The City Manager, subject to any regulations which the Board of City Commissioners may prescribe, shall contract for and purchase, or issue purchase orders for, all supplies, materials and equipment for offices, departments, and agencies of the city government. The Board of City Commissioners shall by ordinance, which may be amended from time to time, set the dollar amount of every such contract or purchase, which may be made by the City Manager, before requiring the prior approval of the City Commission. In no event may the City Manager make purchases or contracts as herein provided in excess of the dollar amount provided for by the then existing ordinance. The City Manager also may transfer to or between offices, departments, and agencies, or sell, surplus or obsolete supplies, materials, and equipment subject to such regulations as the Board of City Commissioners may prescribe.