[z3t4]

Lets say you have 100 TB of data, plus two backups, you are now paying for 300 TB of data.

[Cerium]

I would say that it doubles the cost of backups, but using this math, we start with one copy plus one backup, and add a second backup; that means only a 50% increase.

[Dylan16807]

Also a secondary backup doesn't need to be in hot storage. Coldline or Glacier or similar can easily be a quarter of the price per GB.