In all cases of work to be done by contract, or of the purchase of personal property of any kind, where the amount involved exceed the limit set by state law, unless the council shall by an emergency ordinance otherwise provide, the city administrator or city clerk shall advertise for bids in such manner as may be designated by the council. A contract means as agreement entered into by the City for the sale or purchase of supplies, materials, equipment or the rental thereof, or the construction, alteration, repair or maintenance of real or personal property. Contracts of this magnitude shall be let only by the council, and shall be let to the lowest responsible bidder. The council may, however, reject any and all bids. Nothing contained in this chapter shall prevent the council from contracting for the doing of work with patented processes, or from the purchase of patented applicances. Further regulations for the making of bids and the letting of contracts shall be made by ordinance, subject to the provisions of this charter.