jammerdan Tardigrade is competitive against the costing of the Object Storage you have quoted as long as the aim is not to do much downloading of the data stored. Tardigrade does not have an offering that provides archive storage, such systems often have tape systems within their design to provide vast amounts of capacity, but with slow performance.
nerdatwork Your figures seem about right, but your use case is more that of backing up your NAS rather than the need for an S3 object-store. So the quoted cold storage service would be a better comparison. The real value that iDrive would be providing you will depend on how much you use its advance features such as File Sync and Snapshot/Versioning.