expired Steam Midweek Madness - Portal 2 - $6.79 | Final Hours DLC - $0.68
This was posted 1 year 15 days ago, and might be an out-dated deal
If you don't already have it then I recommend buying it now while it's at 66% off.
In addition to the sale, a new update for the game was just released which adds a map creation and editing feature to the game. Once you have created a map you can publish it to the Steam Workshop and share your creation with the community. You can check out the map editor on the Portal 2 Blog. It looks fairly simple and straight-forward to use.
Sale ends 9AM Friday (AEST)