The proceeds from the sale of said bonds shall be paid to the secretary and treasurer of said board, and shall be by him placed in a separate fund to be known as “permanent improvement fund” to be used and paid out only for the specified purposes in this act [21-8-15, 21-8-16, 21-8-18 to 21-8-26 N.M. Stat. Ann.] enumerated upon order of the board, on checks signed by the president or vice president of said board and by the secretary and treasurer thereof, except such portion thereof as may have been received on account of accrued interest on said bonds to date of delivery, which amount shall be placed in the “interest and retirement fund” for the liquidation of said bonds as hereinafter provided. The cost of preparing, advertising and selling said bonds, including any necessary expense for legal opinions thereon, shall be paid out of the proceeds of the sale of said bonds.