Contracts for the construction and equipping of any joint county medical care facility to be erected under the provisions of this act, shall be let by the board of trustees of said joint county medical care facility subject to the approval of the state department of social welfare. Such work may be let as an entirety or in sections as may be deemed more advantageous. In all cases where the cost of construction exceeds the sum of $500.00, bids shall be advertised in 1 or more newspapers published and circulated within the counties concerned, not less than 2 weeks prior to the date when bids are to be received. Subject to the provisions of this act, the board of trustees of said joint county medical care facility 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 subject to the approval of the state department of social welfare.