The notice of sale may, as an alternative to a single interest rate, permit bidders to name 2 or more interest rates for the bonds proposed to be sold, within such limitations as the notice of sale may provide. In such event it shall state that all the bonds will be awarded to the bidder on whose bid the total loan may be made at the lowest net interest cost to the district, such net cost being computed, as to each bid, by adding to the total principal amount of the bonds the total interest which will be paid under the terms of the bid, after deducting from such interest the amount of premium, if any.