They are running a number of cash rebate programmes here in Australia at the moment. For example they have a $A300 off (~$US210) offer on the D850 at the moment.
I don't think that the rebates are the same across the world from country to country.
I have however seen a lot of cash back offers from all of the major camera and lens manufacturers in recent years and Nikon are no exception here. Add to that a number of post Christmas sales have had a 15% off deal on just about everything, so what with the Nikon rebate and the 15% off, a D850 comes down to about $A3,700 (or ~$US2,600) - this price includes an embedded 10% Goods and Service price, so the pre-GST Tax price is ~$US2,360 on sale priced D850s's with the $A300 rebate. Stock has a genuine Nikon 2 year warranty - so not grey market stock.