That's where I am confused. If the MSRP on a 2TB hard drive is $300, which is what you stated. I assume that you stated the consumer retail price that you could purchase a drive for.
Why would Apple pay that price? They'd buy them by the 10 000 or 100 000s and would probably pay half (or less) than you would as an endpoint-consumer.
Doesn't that not really matter at all either way, a 1TB HDD MSRP is $100 and the 1TB Time Capsule still goes for $500, so if the 2TB MSRP is $300 (that's the price for the OEM from newegg.com) wouldn't Apple still want to maintain their profit margins like they always do and still sell the 2TB for $700?
EDIT: but even if Apple pays let's say half the price for buying in bulk that means they pay $50 for a 1TB HDD and add $450 for other parts and profit, so if they pay $150 for a 2TB HDD add $450 for other parts and profit and you still come to $600 for a single 2TB back up solution, for that price I could get 2 2TB hard drives (or even 6 1TB HDDs) and have redundancy