Downright cheap? I don't think so. What are they, like between $100 and $200 a year? A  cheap 3TB HDD is like $90 to $120 and how long will an off-line drive last?  I say the physical drive will last 20 years or more if only placed on-line once a month.  But I guess a typical person goes about it differently:
I would assume that as they upgrade HDDs to newer faster units or replace them due to a policy based on uptime hours (as in my case), the old ones become the offline storage units.  You can look at this as a zero cost investment quite easily.  And this is also true for a new users setting it up for the first time when he rotates in the backup units 
as the replacements when the hour limit is hit.  Assuming you use at least 3 identical drives in your system (I use 6 identical ones and one system drive) that's three separate external backups on drives you would be throwing away (or selling for $25) anyway. 
That makes the $300 too $500 a cloud service wants over those same three years look pretty expensive to me.  Anyway, I personally  have so many "monthly payments" (bills mostly) the very last thing I need or want is yet another one.  UG! 
