ESPN Basketball reporter, and part-time soccer reporter, Marc Stein, says that the Israeli club have upped their offer to $800,000 and that the USMNT defender wants to make the move, but D.C. United don't want to sell. Likely because he's their best defender and selling him for no reason makes absolutely no business sense.
Without getting into yet another "which league is better?" war, let's think about this logically. No matter what club is coming after Birnbaum, $800,000 isn't that much money in today's game. For reference, Mix Diskerud makes $750,000 a year. Why would a club who has dreams of making the playoffs and possibly winning MLS Cup sell one of their best players for that type of money?
Players have every right to want to move out of MLS and test themselves in Europe, but the league also can't roll over any time a club is looking to bargain hunt for players. There is certainly a price that will get Birnbaum to Europe, but D.C. has every right to hold out for that number, no matter how much the player wants to leave.