Combine this with the "800,000 units to break even on an HD game" and we get a rough estimate of average HD costs. About $21.6 million by the intersection of these two statements, most likely not including any advertising.
PS: This is why DD earns pubs more money on PC than retail, and yes, it does let them set things cheaper than they'd otherwise be forced to. Do you really think PC games would still be $50 new if it weren't for DD?