The price to be paid for such plant, whether gas, electric or both, shall be its fair market value for the purposes of its use, no portion of such plant to be estimated at less than its fair market value for any other purpose, including as an element of value the earning capacity of such plant, based upon the actual earnings being derived from such use at the time of the final vote of such municipality to establish a plant, and also including the market value of any other locations or similar rights acquired by the owners of such plant or plants, intended and adapted for use in connection with such plant or plants, to be sold less the amount of any mortgage or other encumbrance or lien to which such plant or plants or any part thereof may be subject at the time of the transfer of title; but such municipality may require that such plant or property shall be transferred to it free and clear of any mortgage or lien, unless the Superior Court, through its special commission as provided in § 7-228, otherwise determines.