The board of directors of the district may let the contract for such work or materials to the responsible bidder who submits the lowest and best bid or, in the sole discretion of the board, all bids tendered may be rejected, and readvertisement for bids made, in the manner, form, and time as provided in section 70-638. In determining whether a bidder is responsible, the board may consider the bidder’s financial responsibility, skill, experience, record of integrity, ability to furnish repairs and maintenance services, ability to meet delivery or performance deadlines, and whether the bid is in conformance with specifications. Consideration may also be given by the board of directors to the relative quality of supplies and services to be provided, the adaptability of machinery, apparatus, supplies, or services to be purchased to the particular uses required, to the preservation of uniformity, and the coordination of machinery and equipment with other machinery and equipment already installed. No such contract shall be valid nor shall any money of the district be expended thereunder unless advertisement and letting shall have been had as provided in this section and sections 70-637 and 70-638.