The first screen you get to when you log in should show you your predicted monthly cost and current. Failing that you can use the Aws cost explorer to guesstimate how much

edit:

You can also go through the cost and billing manager in Aws.

Edit edit!:

You want to use glacier which is cool, pun very much intended. Plug your estimated usage into cost explorer and you should be good to go.

https://github.com/endrl/jellyfin-plugin-media-analyzer

This fork looks really interesting. I’ve not run it myself but plan on giving it a go soon.