I would say you answered your own question.
Why would you double the cost of a component of your copier when the benefits are negligible?
You mentioned faster access time which is true. Don't you hate standing at the copier while the screen is saying "Please wait, Accessing Hard Drive?"
You mentioned 100% reliable, which is not true. They are certainly more reliable, and there's no concern about drive heads, but once again, not a lot of problems there. The most common issue with hard drives failing is impact. Lots of people drop Laptops. Not many people drop copiers (Art is an exception to the rule).
As far as the "volume purchasing" aspect, that is true, but it is true with the normal Hard Drives as well, and probably to a larger extent.
I have absolutely no data on this, and am only taking a wild shot based upon my experience with previous "new technology" waves, but I'm going to say that if we take your numbers as "Market" then the "Volume" price would be something like $100 vs. $25.