You can use this calculator http://rps.dewin.me/
Storing 45TB of backups even locally cannot be cheap
and when you add off-site additional data center costs to that...
If you're looking for absolutely cheapest way to have off-site backups with your data size (2TB full backups), I would say go with external disk or tape, take those backups home with you, and put them in a fireproof safe. This does add lots of "manual processing" overhead, but also does the job. In fact, that's exactly what we did in early days of Veeam ourselves (although we did not have any "cloud" options at the time yet anyway).