Cheapest option is to buy the game from
Amazon, then use the codes to update your account.
Since Seekers will be released soon, buying the
Seekers Collection and using the 25% code is also an option, but be aware you cannot access the content/codes until its actual release date.
The codes are independent of their platforms, but locked by region.
Edited, Feb 22nd 2013 1:04pm by xypin