I think most places, by now, have their lowest prices set already. Typically they should have ended most other sales or good deals by now to make their black friday sales look that much better. If you want anything lower than what's available right now, you're going to have to wait for black friday.
My suggestion is to find a Toys R Us and buy Halo from there. They have a sale of $10 off for full price games, or $30 off of 2 full price games. With the 2 game deal, you'll end up paying $49 after tax for each of the two games. In my case it was two copies of Halo 4 (mine and a friend's).
Ahh crap, I didn't check the date on your post. Oh well. Just in case you didn't buy it yet, maybe this will help.