Tarsnap charges you for the compressed, deduplicated storage used, so if you’re mostly backing up documents and working files, the amount of storage used is way lower than the raw uncompressed storage. This includes deduplication at a block level.
If you use Backblaze B2 with Restic, you can get the same functionality at a much lower price, but requires more setup.
In the process of moving all my stuff to porkbun as well. It’s the best.