That's not a crazy deal considering the Phenom II x4 840 is actually a "mislabeled" Athlon II (no L3 cache definitive for true Phenoms). The Phenom II x4 955BE is occassionally only $100 and so I'd expect the 840 to be $80. $20 for a game isn't a crazy deal since Steam often does 75% off sales.
It's a decent deal--but not one I'd bite on if I was in the market for a CPU. I'd skip the game and get an unlocked Phenom II x4 (or an Intel).