If Warband is just a counterstrike style multiplayer enhancement as it is now, I don't think charging more than $20-25 for existing owners makes much sense. If more multiplayer modes are added, and multiplayer becomes more tightly integrated with the singleplayer campaign, it becomes a whole new game for me, and would therefore be worth more. Almost every other game that has pure competitive match based multiplayer on top of a strong SP game would have trouble charging for it, and I don't see this as being much different.