What I Would Do If I Ran Tarsnap

Hit the nail on the head with the pricing model. I really want a backup solution like Tarsnap that encrypts my data client-side and has an OSS client. I'm even fine with it being a Unixy command-line tool. But I have almost 1TB--a lifetime, so far--of pictures and music that I want backed up. I have literally no idea how much that would cost with Tarsnap, and it could be as high as hundreds per month. There's no way to find out until the bill comes. So I'm just not going to bother.

If cperciva wants to keep metered pricing, maybe offering a free 3-day trial or something so users can get an idea of how much their particular backup situation would cost before committing would be a good idea.

If you have ~1TB of free space, just create a regular tar archive of your data and compress it -- maybe factor in another 10% for dedup (as seen anecdotally by others with large image collections -- this assumes you have raw images+jpegs -- for just jpegs, maybe nothing). Should be (bounded by) 500 USD first month (storage and upload), and 250 USD/Month after that (and ~250 USD to restore).

I'm not sure what's difficult with these calculations?

The dedup (as I understand it) is mostly relevant for incremental backups "adding up" -- so that you can (mostly) run weekly backups without worrying too much about storage cost ballooning out of control.

Note: I'm not affiliated with tarsnap, nor am I a customer -- partly because I'm in a similar position: The data (emails etc) that I can afford to backup in a similar fashion to tarsnap (I use backupninja as a front-end for duplicity) is almost trivial to backup -- the rest (photos, media) I cannot currently afford to backup to the cloud (nor do I have the upstream bandwidth for it).