Any contract for financial assistance awarded under sections 8-400 to 8-405, inclusive, shall contain the requirement that the state or the authority, as the case may be, shall receive, in exchange for any such assistance, a financial participation in the project. Such financial participation shall be in a proportion which shall not be less than the proportion that the number of low-income units in the project bears to the total rental units in the project. Any sale of the project, any interest in the project or any of its units shall require the approval of the Commissioner of Housing or the authority, as the case may be, and shall be made upon such terms and conditions as the commissioner or the authority, as the case may be, may approve.