Mich. Comp. Laws § 331.205
Contracts for the acquisition or construction and the equipment of any hospital to be acquired, erected, operated and maintained under the provisions of this act shall be let by the board of supervisors of the county. In the case of construction, such work may be let as an entirety or in sections, whichever may be deemed most advantageous. In all cases where the cost of construction or the purchasing of equipment exceeds the sum of $500.00, bids shall be advertised for in 1 or more newspapers published or circulated within the county concerned not less than 2 weeks prior to the date when bids are to be received. The board of supervisors may adopt reasonable rules and regulations concerning the manner of advertising for bids and the letting of contracts. In all cases the right to reject any and all bids presented shall be reserved. Each contract let hereunder shall provide, that the work shall be done or the material purchased subject to the approval of the board of supervisors of the county or by any committee of said board of supervisors selected for that purpose.
MCL 331.205