For things like this, I feel you've got three options. You likely want your data offsite since your primary is onsite, so that means either a cloud provider (G

For things like this, I feel you've got three options. You likely want your data offsite since your primary is onsite, so that means either a cloud provider (Google Drive, Amazon Drive, S3, etc.) which you can choose based on best-price, but as you mentioned, the downside is cost. The second option is to find a friend or family with similar needs, and "trade" storage. You setup a NAS for them to write to. They setup a NAS for you to write to. You both encrypt everything and send it offsite. The upside of this approach is that it's essentially free apart from the allocation of storage space. The downside is that friends and family may not be as reliable as a paid service. A third option is to buy a cheap portable hard drive, and periodically perform backups. The downside of this approach is that it's on you to perform this task regularly, and you'll always have some gap between when your last snapshot was performed and this gap may be meaningful if this isn't conducted with enough frequency.