Amazon is having a sale on Bioshock Infinite at the moment, this is about as cheap as I have seen it anywhere.
Registers on Steam for all you game collectors.
Bioshock Infinite Affiliate link $9.99USD
If you want you can use my affiliate link for the above. (You pay the same I get some of the money Amazon would normally pocket)
You will need a valid US address on your account to purchase digital games from Amazon, personally I choose to stay at the Las Vegas Hilton LVH when I buy games. It has been noted that you should pick an address in a state where Amazon do not charge Sales Tax list here
Waiting for GOY version with all dlc