This from Backblaze takes me back a few years when I had to contribute to a cabinet paper to plan for the purchase of a new disk drive (just one and well less than a gigabyte!).
There is a neat chart demonstrating the difference in cost between what you pay for raw disk units at your mail-order supplier and storage as a consumable. How does a pile of disk drives at us$81,000 become a staggering us$2.8million from EMC or Amazon?
There is also a how-to which is complete down to the rubber bands needed to damp the drive vibration so I expect my geek son to be warming his flat with one of these.