I know it doesn't fulfill the local requirement, but I've been looking into the Cloudberry backup product allows you to pay a one-time fee of $30 (per computer)

I know it doesn't fulfill the local requirement, but I've been looking into the Cloudberry backup product allows you to pay a one-time fee of $30 (per computer) for their software (a free version is also available), and then choose which cloud provider to store the backup on. So you could use Amazon S3 or some other cloud provider to store backups and pay the tiny amount per gigabyte (depending on the storage option you choose). I'd recommend a cloud-based solution as further backup option even if you stick with the local option. I currently back up my NAS using CrashPlan in case a disaster (fire, flood, earthquake, theft, etc) wipes out my computers and NAS. My NAS doesn't need to be exposed to the Internet: the software runs on one of my computers with the NAS connected as network file shares. One of the solutions I'm considering using is Cloudberry Backup. There's a bit of initial cost, because I want the features of the pro version, but cloud storage can be quite cheap in the long run. It can run on a computer and backup network shares just like CrashPlan can. Unfortunately, a local option is not supported. Interestingly, I had renewed my Crashplan subscription only a couple days prior to the discontinue announcement, so I have until October of 2018 to figure out an alternative.