All funds received by the commission shall be deposited in the State Treasury to the credit of a special fund to be known as the "motor vehicle commission fund." All expenses incurred in the organization, maintenance and operation of the commission shall be paid from such special fund. The expenditure of all such funds shall be made only pursuant to appropriation approved by the legislature and as provided by law. The receipts and disbursements of the commission shall be audited annually by the state auditor.