Crusader Kings 2 is a remarkable game which suffers under the yoke of the Paradox DLC strategy - look away for more than a minute and suddenly there’s eight hundred dollars of content that you missed.
The current Humble Bundle gives you the base game and all the expansion packs (including the most recent one, released this last December) for fifteen bucks.
CK2 deals pop up with relative frequency, but this is astonishing value even if you already own several of the packs in the bundle.