Subnautica is an open world, underwater exploration and adventure game currently under construction at Unknown Worlds. The game is in advanced stage of Early Access development, with substantial content available for play. Performance/frame-rates, stability, and polish are not yet up to the standards of a finished game.
According to IsThereAnyDeal, it's at the lowest price. It can be played on PC, MAC and supports VR platforms such as Vive, Oculus and OSVR.
Australian price is estimated with Google.