On security, I'd like to point out that GCS now supports Customer Supplied Encryption Keys [0]. If you lose your key, we can't help you. Nobody can just unwrap your encrypted data.
On cost, I'm using Nearline myself ($.01/GB/month so about $10/TB/month) as an offsite backup of my home NAS setup. Paying for actual bytes stored instead of bytes of capacity gets you at least 20% (raid overhead) but honestly closer to 50% or more depending on how full you are. The poster above had about 3 TiB apparently which works out to $30/month. That's pretty good for an unthrottled replicated storage system offsite.
(And like you, I'm considering making my media directly read-only available via App Engine or something, because once you're talking about 1+ TiB of photos all photo hosting sites fall over).
On cost, I'm using Nearline myself ($.01/GB/month so about $10/TB/month) as an offsite backup of my home NAS setup. Paying for actual bytes stored instead of bytes of capacity gets you at least 20% (raid overhead) but honestly closer to 50% or more depending on how full you are. The poster above had about 3 TiB apparently which works out to $30/month. That's pretty good for an unthrottled replicated storage system offsite.
(And like you, I'm considering making my media directly read-only available via App Engine or something, because once you're talking about 1+ TiB of photos all photo hosting sites fall over).
Disclosure: I work on Google Cloud.
[0] https://cloud.google.com/storage/docs/encryption