Section 36. Said commissioners may erect on said land such temporary buildings of inexpensive construction as they consider necessary for the proper housing of prisoners and for other purposes, in no case, however, costing over three thousand dollars. If the land reclaimed, cultivated and improved, as aforesaid, shall be sold, the proceeds shall be placed in the county treasury and used, so far as possible, for the payment of loans made under section thirty-eight. Any surplus thereof shall be used for general county purposes. The commissioners may appoint, and at any time remove, a superintendent for said farm and such assistants as in their opinion are needed for its proper management. No building used for housing the prisoners shall be constructed until the commissioner of correction has approved the plans therefor.