Revenue bonds and warrants may be sold by negotiation or by public or private sale in any manner and for any price the legislative body of any city or town deems to be for the best interest of the city or town. Such legislative body may provide in any contract, for the construction or acquisition of the proposed facility or utility or the maintenance and operation thereof, and that payment therefor shall be made only in revenue bonds and/or warrants at their par value.
RCW 35.41.060