The proceeds of bonds sold pursuant to Section 69-5-17 shall be paid into the state treasury to the credit of a special fund known as the State Fair Fund, and shall be used solely for payment of the cost of the project or combined projects, and shall be disbursed upon order of the State Building Commission under such restrictions, if any, as the resolution authorizing the issuance of the bonds may provide. Provided, however, that any surplus in the State Fair Fund over and above the requirements to meet the payments on outstanding bonds and interest thereon when due may, in the discretion of the State Bond Commission, be invested in United States Government bills, notes or bonds, Mississippi General Obligation Bonds, Mississippi Revenue Bonds, Mississippi State Highway Bonds, or in bonds of any municipality or any county in Mississippi; and, upon the sale thereof, the entire proceeds of the sale, including all earnings from the investment, shall be paid into the State Fair Fund. If the proceeds of bonds sold pursuant to Section 69-5-17, by error of calculation or otherwise, shall be less than the cost of the project or combined projects, unless otherwise provided in the resolution authorizing the issuance of the bonds, additional revenue bonds may in like manner be issued to provide the amount of such deficit which, unless otherwise provided in the resolution authorizing the issuance of the bonds, shall be deemed to be one of the same issue and shall be entitled to payment from the same fund without preference or priority of the bonds first issued for the same purpose; provided, that in no event shall the outstanding bonds total more than Seven Hundred Fifty Thousand Dollars ($750,000.00). 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.