I heard that last year Esquire Magazine included eink displays on the front of the their covers. It wasn't a really good one, it only flashes a few text, but it showed that it's cheap enough to be inserted into a $6 magazine.
If you look up online the price of screen replacement for ANY electronic is overly priced. Sometimes the screen replacement for a laptop cost more than half of the laptop itself. It's just the price you have to pay since there's a small market for it.
I would guess the eink display would cost the manufacture somewhere around $30 to $60.