Arma 3 has entered beta, and you can purchase your way in if you just can't wait for the full version. The beta comes in three packages, all of which will unlock the final version once the game releases. If you're already in from the alpha, however, you don't need to pay to get in the beta.
Two of the versions are available on Steam (via Polygon). A $44.99 basic package simply unlocks the beta. For $59.99 you get the Digital Deluxe Edition, which includes a digital soundtrack, maps, a tactical guide, and Arma: Cold War Assault.
An even pricier Arma 3 "Supporter Edition" is available through the official site. That one includes all of the Digital Deluxe bonuses, a copy of Arma X: Anniversary Edition, a special badge for the Bohemia forums, and all future DLC for Arma 3. That one will run you $91.99.