The Witcher 2: Assassins of Kings Enhanced Edition is currently available for $4 through CD Projekt Red's own GOG online store. That's an 80 percent markdown. By comparison, the game is selling for $20 right now through Steam.
The deal is part of a special promotion called Battle of the Games, which also sees markdowns on games like the original Witcher ($2), as well as Heroes of Might and Magic ($2.50), Heroes of Might and Magic II ($2.50), Heroes of Might & Magic III ($2.50), and Blackguards ($22.50).
The special prices expire tomorrow, at which point GOG will launch another sale on a set of games. GOG users can vote for which set they would like to see discounted. One set includes Chaser, Red Faction, and Red Faction 2, while the other includes Unreal 2: The Awakening, Unreal Gold, and Unreal Tournament Game of the Year Edition.