Any municipal bidding procedure may be waived by the city council or board of public works of a city of the first class (1) when materials or equipment are purchased at the same price and from the same seller as materials or equipment which have formerly been obtained pursuant to the state bidding procedure in sections 81-145 to 81-162, (2) when the contract is negotiated directly with a sheltered workshop pursuant to section 48-1503, or (3) when required to comply with any federal grant, loan, or program.