For backing up something personal, why don't you just use actual Backblaze?
[1] https://help.backblaze.com/hc/en-us/articles/217664898-What-...
B2 is 400% more expensive than Deep Archive. Whether the lower transfer costs result in savings depends on your use case. For B2 the cost of transfer is 5x a month of storage, for Deep Archive it’s 90x.
GCS is also cheaper than S3, with even higher transfer costs, but instant access irrespective of storage class.
https://aws.amazon.com/blogs/aws/aws-storage-update-s3-glaci...
I do indeed use B2 for my personal Linux backups