I'm somewhat tempted by B2 but $5/TB/mo feels a bit steep for a NAS.
For me that would be about $100/mo, and for OP that's $25/mo. It would only take a few months before buying a drive for off site cold backup would be more cost effective.
Considering their personal plan is $7/mo for unlimited TBs, it really invites hobbiests to find workarounds after their first TB. Unless I'm missing something.