Neb. Rev. Stat. § 31-512: Neb. Rev. Stat. § 31-512

All contracts for work to be done, the expense of which is more than fifteen hundred dollars, shall be let to the lowest responsible bidder, upon notice, of not less than twenty days, of the terms and conditions of the contract to be let. The board of trustees shall have power to reject any and all bids and readvertise for the letting of such work.