Work relief projects conducted pursuant to Section 17200, which consist of the work of repairing or maintaining any shipping facility or public building, shall not be subject to the competitive bidding provisions of Sections 25450 and following of the Government Code where the work is to be done entirely by indigents, except that those providing supervision need not be indigents. In counties employing a purchasing agent, the materials and supplies used in such a project may be purchased by the purchasing agent without limit and without the formality of obtaining bids, letting contracts, preparing specifications, and the other formalities otherwise required by law.