The department of transportation is authorized to enter into rental or leasehold agreements under which the department shall acquire title to such buildings within a period not exceeding thirty years upon payment of the stipulated aggregate annual rentals. The plans, specifications, bids, and contracts for such buildings and the terms of all such rental or leasehold agreements shall be approved by the governor, the chief engineer, a majority of the members of the commission, and the director of the office of state planning and budgeting. The rentals shall be paid solely out of the state highway fund, and the obligation to pay such rentals shall not constitute an indebtedness of the state or be paid out of any other fund. Such rental shall be included in the annual budgets of the department and shall be certified, audited, and paid in the same manner as all other accounts and expenditures payable out of said state highway fund.