NISA has opened pre-orders for Natural Doctrine on their webstore, including both the Standard Editions and Limited Editions for each of the three platforms. Each Limited Edition includes a softcover artbook, tear-resistant poster (23"x13"), and an 'Explorer's Bag'.
The standard editions are priced at $39.99, $49.99, and $59.99 for PlayStation Vita, PlayStation 3, and PlayStation 4 respectively. The Limited Editions are marked at $59.99, $69.99, and $79.99. Or in other words, twenty dollars higher for the Limited Edition bonuses.
The listing also outs a release date of September 16th for Natural Doctrine in North America. The game is also set to release in Europe sometime this Fall.
Update: Natural Doctrine is set to release in Europe on September 19th.