They've cut some fairly shallow corners, like mono vs color cameras so I imagine getting it within a decent price range has been of high importance. I really doubt it'll be any thing close to $1k.
I think it’s possible that there’s a technical reason for monochrome cameras. For example, to let in the maximum amount of IR light for tracking. Bayer filters reduce the amount of light getting in, so it might help the IR LEDs be visible on surrounding walls in the dark.
