All money received by the Commission from the sale or lease of any property, in excess of the amount expended by the Commission for authorized purposes under this Act shall be paid into the State treasury for deposit into the Mid-America Medical District Income Fund. The Commission is authorized to use all money received as rentals for the purposes of planning, acquisition, and development of property within the District, for the operation, maintenance, and improvement of property of the Commission, and for all purposes and powers set forth in this Act. All moneys held pursuant to this Section shall be maintained in a depository approved by the State Treasurer. The Auditor General shall, at least biennially, audit or cause to be audited all records and accounts of the Commission pertaining to the operation of the District.