Notwithstanding any other provision of law, all purchases and contracts made by the administrator or the Secretary of the Army for supplies or for services except for personal services, shall be made after advertising, in such manner and at such times, sufficiently in advance of opening bids, as the administrator or Secretary of the Army, as the case may be, shall determine to be adequate to insure notice and opportunity for competition. Such advertisement shall not be required, however, when (1) an emergency requires immediate delivery of the supplies or performance of the services; or (2) repair parts, accessories, supplemental equipment, or services are required for supplies or services previously furnished or contracted for; or (3) the aggregate amount involved in any purchase of supplies or procurement of services does not exceed $500; in which cases such purchases of supplies or procurement of services may be made in the open market in the manner common among businessmen. In comparing bids and in making awards, the administrator or the Secretary of the Army, as the case may be, may consider such factors as relative quality and adaptability of supplies or services, the bidder's financial responsibility, skill, experience, record of integrity in dealing, and ability to furnish repairs and maintenance services, the time of delivery or performance offered, and whether the bidder has complied with the specifications.