A quick update on the Nikon D850 shipping situation in the US: Amazon is now shipping pre-orders placed on October 7th. B&H is still fulfilling pre-orders placed at the end of August. Adorama just shipped a camera ordered on September 5th. On eBay the D850 prices are still around $4,000. Wex Photo in the UK currently has an open box Nikon D850 camera.
Nikon D850 pre-order links: B&H | Adorama | Amazon | BuyDig | BestBuy | Cameta Camera | Focus Camera | eBay | WEX | Jessops