"This large"? All we know about it at this point is that it's a single new quest zone and a modest level increase. If it weren't for the level increase, there would be no differentiation between it and the standard major content patch that MMO games tend to get twice a year or so. The reason expansions for other games tend to cost ~40 is because they actually add significant features to the game, like classes, races, crafting skills, etc. We have no reason to believe that ROHTC will have anything like that.