That pricing sounds waaaay too low to me; these are big, cutting edge parts, basically unobtainium at the moment unless you have a close relationship with Xilinx. When they reach the channel they will not be cheap either.
I checked pricing for qty 1 via digikey.com in USD, choosing the part that was about $2k as it seemed closest to the specs I could find mentioned in the joint Xilinx/Amazon announcement .
You must have been comparing to something else entirely! The cheapest Ultrascale part that Digi-Key carries is XCVU065 at $6800, and that isn't even in the right part family.
Might have been confused by the part number; I think the Kintex series is closer to the $2k range, so that might be the confusing culprit.