Warhammer 40k Dawn of War II: Gold Edition is on sale right now on Amazon
for $4.99 - 83% off. This includes the base game plus expansion "Chaos
Rising." These are Steamworks games therefore are required to be activated
on the Steam client to play.
I believe this is the cheapest this has been both on Steam as well as other
sites.
Link: http://www.amazon.com/Warhammer-40-000-Dawn-War/dp/B0047T7UFI/r