I would like to know what estimates are reasonable for data storage
costs. Ideally, there would be industry estimates for data stored in
an off-site facility and the cost for a firm to host this itself.

I am looking for the following info:

a) What's a good estimate for cost per TB for an external solution
(assume that the company with the data has a sufficient internet
connection)?

b) What's a good estimate for cost per TB for an internal solution (all costs)?

c) What are the cost trends expected over the next decade? Is the cost
per TB expected to decline by X%?

Also, if there are certain levels at which these cost estimates are
not good that would be useful. In each case, Quality of Service is
more important than Price so this would be important. I am expecting
that this answer will be relevant for US settings, but if there is any
difference between Canada and the US that would be helpful (I am
interested in applying this information in Canada primarily).