Starting on October 7th, the Xbox One Kinect will be available separately for $150 USD bundled with Dance Central Spotlight.
Originally packaged with the Xbox One causing the console to be $499.99 on day one, Microsoft removed the sensor in June to bring the price of their new console to $399.99; on par with the PS4. Since then, Xbox One's sales have presumably gone up although Microsoft has yet to release their sales numbers since a few months ago stating they'd reached 5 million sold to retailers. They have, however, stated their sales doubled from May to June.
We didn't find too much use for the Kinect sensor here but others may find this individual price worth a future purchase.