Here's a weird one for ya ... you can purchase the Mafia 2 digital download from Amazon video game download section for $12.50 here:
http://www.amazon.com/2K-Games-40465Mafia-II-Download/dp/B004774ISM/
... and then immediately after purchase, visit your purchased game section, show your retail key, hop onto Steam then activate the game on steam. I just tried it and the game activated flawlessly for me and is now downloading on Steam. The game is listed on Steam for $33.49 which nets you a $21.00 savings!
YMMV, not sure how long this will work or if this is permanent but it did work for me.
http://www.amazon.com/2K-Games-40465Mafia-II-Download/dp/B004774ISM/
... and then immediately after purchase, visit your purchased game section, show your retail key, hop onto Steam then activate the game on steam. I just tried it and the game activated flawlessly for me and is now downloading on Steam. The game is listed on Steam for $33.49 which nets you a $21.00 savings!
YMMV, not sure how long this will work or if this is permanent but it did work for me.