The proceeds of such bonds shall be paid into the county treasury to the credit of a special fund known as the industrial development authority construction fund, and shall be used solely for payment of the cost of the project except as hereinafter provided, and shall be disbursed upon order of the authority upon such restrictions, if any, as the resolution authorizing the issuance of the bonds may provide. If the proceeds of the bonds of any issue shall exceed the amount required for the purpose for which the bonds were issued, the surplus shall be paid into the fund established for the payment of the principal of and the interest on such bonds.