$800 sounds about right. I am thinking it will be lower to sell better but
The headset itself $399
The external box for the extra processing power another $299 (yes there is an external box to boost processing power).
As others have said, you are way off base with the external box. Sony has been clear about what it does: it takes the VR image that the PS4 sends it, and removes the VR warp so that it will look normal on a TV set (so that the VR is mirrored to the TV so others can see what you see). That and it does some simple audio processing. That's it.
And the $800 has been known to be false for a long time, that's a really old rumor. If the PSVR is $800 US (without being part of a console package), I will eat my Oculus Rift.