No freakin way. Thats impossible.  It should be 300-550 depending on who sells it but thats just plain scamming. Did you tell them your P/N or part number so they can give you the 4k upgrade for it?
I ordered x17 R1 with FHD 360Hz G-Sync and It performs really well in every game, super smooth and no tearing. But after using it for a month, I kind of want the 4K 120Hz display variant for better image clarity. I have contacted Dell, they said I can switch the panel to 4K but need to wait for about 2 months due to part shortages. Still I want to confirm whether its possible to upgrade from FHD to UHD?
x17 R1, 4K upgrade