Valve Game Sale at GameStop. Portal 2 $10.19 By w00py | June 12, 2012 0 Comment There’s a Valve Game Sale going on at GameStop. Portal 2 is the daily deal for 6/12 at 66% off. Portal 2 = $10.19 Definitely uses Steamworks. Requires Steam. Keep in mind a Steam Summer sale is set to start any time soon.