A $25/TB drive is not the only expense that $5 goes towards:

* there's actually probably 2 or more HDs holding that TB, since the business is promising that the data won't be lost

* theres the computer(s) that hold that HD.

* theres the electicity, bandwidth and space rental costs for those computers

* theres the cost of employees to make sure that the computers keep running.

* theres the cost of the marketing so that you know that the service is available

* theres all the book-keeping, taxes, cc fees, etc that need to be paid on the recurring charge

* there's (hopefully) profit for the investors/owners

and so on.

Also, on your side you should consider several of those factors yourself to do the comparrison:

* how much do you consider the time spent managing your hdds to be worth? (if you're a business this is employee-hrs, if you're talking about for yourself privately, there's still a value you should attach to your own time)

* do you have backups? If so, what does it cost to put them offsite? (In terms of space rental or favors traded, and your time)

* electricity, etc

* how much is it going to cost you to learn to reliably store your data (in terms of up-front cost, time spent, etc)

* and of course hard drive costs