Cost is $7 per month.
I hope for Monte that people expect less for those $7 than what they expect from the DDI subscription.
The rules supported will be primarily 3.5, but let me offer up two thoughts in that regard. The first is, even as I'm writing this I'm struck by how rules-light it all is. It would be a piece of cake to use it with any edition (older or newer) of the game. The second is, if I discover that a large percentage of the membership is using another rules system, like say Pathfinder or Arcana Evolved, I'll make a point to offer up frequent conversion information, assuming that I can do so legally, respecting copyrights where needed.
It's a team of one. Just me (although I have the excellent and award-winning cartographer Ed Bourelle, the excellent and award-winning editor Sue Cook, and a bevy of excellent--and in some cases award winning--artists to back me up).
That said, while the updates to the site will be produced by me (with member input and opinions weighed in), there will be much encouragement and ample space for members to contribute their own supplementary material.