IIRC, they don't go in the general ticket sale anymore. You enter the sweepstakes to have a shot at buying tickets (no guarantee). They are the hottest tickets at the park of which they sell out every game. The tickets are now $165 - the highest in the park.
http://boston.redsox.mlb.com/bos/tic...ng_pricing.jsp
Green Monster standing room tickets are $35, so you can expect to pay $75-$100 probably through Ace Tickets or Stubhub. These tickets are quite good as the concession areas up there are not crowded, there is plenty of place to stand in the last row, or along the railing towards center field.
I have sat in a seat up there and had standing room, and the novelty is great, but you can not see anything in left field and the view to center is not great either. Of course in Fenway, a lot of seats having viewing issues.