Damn you Googlebot!
The plug-in's not even out yet. That page has been sitting on the site, not linked into anything for a few weeks while we make the installers, finish the manual, and exorcise the last ghosts in the machine. Not sure how Google picked it up.
Anyway, it'll be free to anyone who owns the complete BIGBox set. We're not offering it for sale at this time.
Not the way I wanted to announce it, but there you go.
We'll have some more information, screenshots, etc. when it's officially released.