A school district may use state funds received under this subchapter to pay the principal of and interest on refunding bonds that:
(1) are issued to refund bonds eligible under § 46.003;
(2) do not have a final maturity date later than the final maturity date of the bonds being refunded;
(3) may not be called for redemption earlier than the earliest call date of the bonds being refunded; and
(4) result in a present value savings, which is determined by computing the net present value of the difference between each scheduled payment on the original bonds and each scheduled payment on the refunding bonds. The present value savings shall be computed at the true interest cost of the refunding bonds.