If you follow a referral link (I believe the OPS link is a referral) and sign up under him, once you spend $5 on the site both you and he will receive a 5$ credit.
I bought Magicka and the Marshlands DLC for 5.43, and received a $5 credit. I used that to buy Magicka Vietnam.
Base game + 2 DLC packs for 5.43. All activated on Steam.