Before entering a contract under section 48-05-11, a governmental unit shall submit a request for proposals. The time period between the request for proposals and the due date for proposals may be no less than fifteen business days. Upon receipt of the request for proposals, the governmental unit shall evaluate all proposals from qualified providers which include estimates of all costs of installations, modifications, or remodeling, including costs of design, engineering, installation, maintenance, repairs, or debt service, and estimates of the amounts by which energy or operating costs will be reduced.