As many others have said, AWS have a pricing calculator that lets you determine your likely costs.

As a rough calc in the tool for us-east-4 (Ohio), if you PUT (a paid action) 1,000 objects per month of 1024MB each (1TB), and lifecycle transitioned all 1,000 objects each month into Glacier Deep Archive (another paid action), you’ll pay around $1.11USD per month. You pay nothing to transfer the data IN from the internet.

Glacier Deep Archive is what I use for my backups. I have a 2N+C backup strategy, so I only ever intend to need to restore from these backups should both of my two local copies of my data are unavailable (eg. house fire). In that instance, I will pay a price for retrieval, as well as endure a waiting period.