The prevailing class II price for the second preceding month for purposes of making partial payment for milk pursuant to section 258-b(2)(a) of the law shall be the class II or equivalent milk price announced for the applicable Federal or State milk marketing order. A milk dealer not subject to a Federal or State milk marketing order shall make partial payment at not less than the class II price announced for the New York - New Jersey milk marketing order (Parts 19 and 20 of this Title).