When I went to Eretz Yisroel for a summer BH"Z, I somehow got an apartment from a friend's friend's friend in The Mir who was coming to the US for BH"Z for a very decent rate; basically covering their rent & utilities for the month.
It would seem that that is the best way to find apartments there. If someone on DDF goes to The Mir, or Rav Shalom, or any of the other Yeshivos that may have Yungerliet coming to US for BH"Z and hangs up signs, they can charge a fee to make it worth their time, and it will still be much cheaper than the vacation rentals.