I found some US sites selling them for $270, some others for $320 so I guess it depends on where you look.
Something I hadn't considered, though, is that The One kit looks much shorter than a standard impy/bushy, looks as though the solenoid is contained within the grip instead of a tray, so that should leave it about 1/2" lower! That could be a factor worth considering.
Edit: Bear in mind that the BKO also comes with an inline reg, which is something you'd have to add to The One.