Tarsnap won't be able to shrink your photos by using deduplication and/or compression. I guess users paying 10$/mo with terabytes of data stored, have massive advantages of both, but it all depends on your usage.
If you are going to store 100GB of photos with Tarsnap, I'd guess it would be close to 25$ as you said. If you just want your photo collection for disaster recovery, you could check out Glacier instead, which is a lot cheaper.
If you are going to store 100GB of photos with Tarsnap, I'd guess it would be close to 25$ as you said. If you just want your photo collection for disaster recovery, you could check out Glacier instead, which is a lot cheaper.