That's the retail cost, not the production cost. Of course it's going to cost twice the amount at consumer level but from a manufacturing one, there is very little difference. If Sony and Microsoft included 2tb models right off the bat and kept the unit price the same or slightly raised, that would cut the thriving wholesale drive market in half. They will not throw their own suppliers under the bus especially when there is a market to be milked for the next few years.
This market along with peripherals is the real money maker so they will not show their hand for a while yet but in two years time, the same drives costing the same to produce as they are now will be sold in higher capacity at 30%+ off with no loss incurred - just shrunken margins.
The difference in the drives may be twice the capacity but to make them, it makes very little difference. There are still low-spec hard drives being built right now that cost more to make than a top-end, high capacity SSD.