Currently sitting at $15.95USD rather than the $30 it is meant to be selling for. http://store.steampowered.com/app/218560/
Can’t get enough Borderlands 2? Grab the Borderlands 2 Season Pass and get access to four downloadable content packs for Borderlands 2 at one discounted price:
Includes access to four brand new individual add-on content campaigns for Borderlands 2 as they become available.
Add-on content packs are scheduled to be released following the game’s launch through June 2013.
Each campaign will feature several hours of gameplay and introduce new adventures, allies, enemies and environments.
You can't buy it for yourself but you can buy it as a gift, store it in your inventory and gift it to yourself when the game comes out.