Amazon S3 cloud storage fees are around $0.15/GB per month.
You can use simulation mode to calculate how much uncompressed data TKLBAM is going to store in a full backup:
$ tklbam-backup --simulate CREATING /TKLBAM FULL UNCOMPRESSED FOOTPRINT: 148.30 MB in 6186 files
In practice, the actual footprint of a full backup will usually be smaller due to compression, but this depends on the type of data being compressed (e.g., text compresses very well, video very poorly).
By default, a full backup is performed if one month has passed since the last full backup. In between, incremental backups will be performed which only record changes since the last backup. The full backup frequency can be customized. See the manual page for details.