The Xbox One is currently in high demand with Microsoft struggling on the supply side of the equation. Amazon has currently has relisted the Xbox One back in stock for $499.99 without any of the extras. If you want one for Christmas or want to gift one for Christmas, it may be a good idea to grab one now.
You may also want to read this blog post by Major Nelson with some tips on how to grab to an Xbox One. He recommended two tracking sites to use:
Buy Now: Amazon
Update: Well the consoles sold out fairly quickly.
Update #2: Back In Stock