(1) If after the hearing the supervisors or board of county commissioners decide to proceed with the improvement, they shall let the contract for the construction of the work as a whole or in parcels as they may deem best. They shall give notice of the time and place the contract or contracts will be let by publishing for three successive weeks in one or more weekly newspapers published in the county, which notice shall state the specifications, nature, and extent of the improvement, the time within which the work is to be completed, and the allotment or allotments to be let. Sealed proposals shall be received and the work let to the lowest and best responsible bidder. Except as provided in subsection (2) of this section, a bond, in form prepared by the supervisors or board of county commissioners, conditioned for the faithful performance of the contract and executed by the bidder and surety or sureties to the county and to all parties interested in the amount of the bid, shall accompany such bid.

(2) If a contract, the provisions of which are limited to the purchase of supplies or materials, is entered into pursuant to this section and if the amount of the contract is fifty thousand dollars or less, an irrevocable letter of credit, a certified check upon a solvent bank, or a performance bond in a guaranty company qualified to do business in Nebraska, as prescribed by and in an amount determined by the county board of supervisors or commissioners, conditioned for the faithful performance of the contract and executed by the bidder to the county and to all parties interested in the amount of the bid, shall accompany the bid.