Section 14C. The agreement made under section fourteen B, or any amendment to such an agreement, may contain provisions authorizing any member town to sell, lease or grant a license to use any school building and any land appurtenant thereto or used in connection therewith to the regional school district, and any such town may authorize such sale, lease or license accordingly, notwithstanding the provisions of section three of chapter forty or any other provisions of law to the contrary. In case of a sale, the price and time or times of payment and the method by which the towns other than the selling town shall be assessed for such payment shall be set forth in the agreement or amendment; but in no case shall payments be made which shall extend over a period in excess of twenty years. In the case of a lease or license to use, the rental or license fee and terms of payment and assessment shall be set forth in the agreement or amendment. The lease or license to use may be for a term or period not in excess of twenty years, and may contain provisions for the extension of the lease or license to use for an additional term or period not in excess of twenty years, at the option of the regional district school committee.