When any town has determined to construct or reconstruct any highway, section of highway or bridge, which construction or reconstruction is to be paid for from funds allotted to such town under the provisions of sections 13a-175a to 13a-175f, inclusive, and the commissioner has entered into an agreement with the selectmen of such town, as provided by sections 13a-175e and 13a-175f, said commissioner shall call for bids and award a contract for such construction or reconstruction in the manner provided by section 13a-95, except that, if, in the opinion of said commissioner, it is to the best interest of the state and such town, the commissioner may award to such town a contract for such construction or reconstruction upon such terms and conditions as the commissioner determines, provided the estimated unit prices under any contract so awarded shall not be in excess of ten per cent more than the average unit prices prevailing during the preceding twelve months for similar work in the state and provided such town shall have authorized the selectmen to enter into such contract in the name and on behalf of such town. Nothing in this section shall be construed to eliminate the use of force account work for the repair of town aid highways. The commissioner may, subject to the approval of the selectmen or legislative body of such town, enter into an agreement with a third party for additional construction or reconstruction works when requested to do so by such third party, provided such third party shall, immediately upon certification by the commissioner, pay to the State Treasurer the full cost to the state of such additional construction or reconstruction works. If under such agreement such additional construction or reconstruction works are carried out by such third party, they shall conform with all requirements and regulations of such town and such as may be prescribed by the commissioner.