To pay the cost of purchasing or constructing a natural gas system under this subchapter, the county may issue bonds payable from and secured by a pledge of the net revenue of the system. The cost of the system may include:
(1) legal, fiscal, and engineering expenses;
(2) interest that accrues during the construction of the system; and
(3) the cost of supplying gas under Section 1477.119, including any increase in the cost of distribution lines or facilities.