No purchase of real property shall be made unless a notice of the intention of the board to make the purchase is published for at least three weeks prior to the purchase in a newspaper of general circulation published in the county where the property is to be occupied. If no newspaper is published in the county, the notice shall be posted at least three weeks prior to the time the board meets to consummate the purchase in at least three public places in each supervisorial district in which the property is situated. The notice shall contain a description of the property proposed to be purchased, the price, the vendor, and a statement of the time when the board will meet to consummate the purchase.