I have circa 9TB of files...
What I am planning to do is burn all the media etc to DL Blu Ray disks (which cost about $8 locally for good ones, but can be imported in 100+ quantities for around $3.40 each incl shipping). Then store those offsite. I will burn a new disc every 7-10 days as material is added.
While burning around 180 discs will be a pain in the backside, I will spread it over 3-4 months, and the cost should only be around $600. Then ongoing cost of about $110 per annum to keep up with media additions. I will use re-writable discs to snapshot the changing data directory.
Phew! That seems like a lot of hard work. I think I would just buy 4 or 5 2TB portable HDDs. Similar price, more flexibility, reusable, and can backup 2TB each without user intervention. Even cheaper if you buy 2TB desktop HDD's.
Then store off site, and hope you never *need* to use them. The last drive can freshened from time to time with something like "FreeFileSync" to keep recent data updated.