MTA greenlights whopping $1.9B contract for long-awaited Second Avenue subway — and transit officials still claim it’s a savings

The money train never stops. The MTA awarded a nearly $2 billion contract on Monday for the long-promised Second Avenue Subway’s next phase — a colossal payout that transit officials claimed was a solid investment even as the existing system crumbles. The transit agency’s honcho Janno Lieber when asked by The Post why the Metropolitan…