Whenever the board of county commissioners deems it advisable they may proceed to advertise and let the contract for the enlarging or remodeling of such building in the manner now provided by law. If at such time there are insufficient moneys in the special fund, the board of county commissioners may issue bonds of the county in an amount which together with the amount raised by the levy authorized by this act will not exceed the total amount stated in the resolution of the board of county commissioners. All such bonds shall be issued, registered, sold, delivered and retired in accordance with the provisions of the general bond law. Nothing in this act shall prevent the use of any available federal or state aid or both by the county in carrying out one or more of the purposes authorized by this act.