The county board of each such county shall have no power to borrow money for the acquisition or construction of any such toll bridge or bridges except as in this Division of this Article provided and all money borrowed and obligations incurred by each such county in the acquisition or construction, and in the repair, maintenance and operation of each such bridge shall be payable solely and only from the revenues derived from the operation of each such toll bridge.
     All contracts for the construction of any such bridge and its approaches involving the sum of $500 or more, shall be let to the lowest responsible bidder therefor after notice inviting bids shall have been given by the county board. Notice inviting bids shall be published at least once in a daily or weekly newspaper, published and of general circulation in the county, the date of publication to be not less than 15 days prior to the date set for receiving bids. The county board shall have the right to reject all proposals or bids submitted, in which event a new date must be set for receiving bids and a new advertisement inviting bids published, as required in the first instance.