Meh, I have a feeling that they're free. Wouldn't be a proper award for it to cost money......well, more money than that you spent on the game in the first place.
A also have a feeling that over time, there will be awards for every game......as I understood the video they had out before the update that told you about it, there will be weekly updates for it. Of course, the big games go first, like Halo and Gears and such. And I'm sure the smaller games won't have much too offer, either. Maybe a t-shirt. But something.
Right now, the only awards that I'm thinking about are the one OXM mentioned for Halo 3's Overkill achievement, if it'll just be something with the medal on it, or something unrelated, and when Banjo/Perfect Dark's awards will come out. After all, they made the avatars in the first place.......if I remember right.
No, Luke. I killed Mufasa!