Mich. Comp. Laws § 120.27
No port district coterminous with a county, or comprising an area greater than a county, shall be empowered to make any expenditure or any commitment for the expenditure of funds, arising from any source whatsoever, except to the extent that the same shall have been first duly authorized by the port district budget committee if there be one and specific appropriations made by the board or boards of supervisors of such county or counties: Provided, That nothing in this act contained shall be construed as preventing a port district from making any expenditure or commitment, or performing any act, required by any statute or by the terms of any ordinance or resolution pertaining to the issuance of revenue bonds, if such issuance was approved by the board or boards of supervisors as required in section 16 of this act. In all cases involving the expenditure of $1,000.00, or more, each port commission shall enter into contract with the lowest competent and reliable bidder for all work to be done and for the purchase of all supplies and materials required by the port district.
MCL 120.27