This may have been mentioned in the Amazon digital deals thread but currently NBA 2K14 is $7.50 for the digital download which is redeemable on Steam. What makes this interesting is that if you bought a digital PC game published by 2K from Amazon prior to it's October 2013 release you may have gotten a $5 promotional credit towards pre-ordering the PC copy of 2K14. I got credits for 2K games purchased as far back as December 2012. If you're an email hoarder like me I received the emails notifying me of the credits on 9/25/13 and is a mostly generic promotional credit email (aside from mentioning it was to pre-order 2K14) with the subject "Your Amazon.com Promotional Credit". If you earned it the credit should be in your account still (it expires September of this year) and apply when you go to checkout the digital copy.
Additionally I received a $5 credit for the Amazon Android app store for purchasing 2K14. There's no mention of that on the 2K14 page but I received the email notifying me of the credit with the purchase email for 2K14. App store credit expires July 31, 2014.