The price on the pallets has been set for over a week now. It doesn't mean anything. A week ago BTC was at $20k USD and they will adjust it based on the price of BTC (as they have stated) at the time of sale. Right now I expect it to be less than the price they are showing.
Pure and simple: they can charge whatever they want and (at least some) people will pay it.
So at today's pricing you can take off around $390.15. But this does not account for shipping/import taxes etc....
Edit: Yes, they can most likely charge 4k, and still sell out. People will still snatch them up
Bitmain's S9 batch that sold out on Dec 19th was priced at $2750, the batch that sold out the other day was at $2340. I would expect the 821s to be priced under 3k, assuming the price of BTC/BCH doesn't go through the roof before the 12th.