Seeking recommendations for a backup storage solution

Our tape system is failing and I need to put together a backup storage solution at as low of a cost as is reasonable. The important points are listed below:

• Preferably a backup to disk solution, either a NAS or SAN (if SAN, I need to be able to justify the additional costs in terms that will be beneficial to the company)
• Our backup strategy with the tapes was as follows:

1. Weekly full backups (past two weeks kept at all times) - roughly 5 TB in size
2. Daily differential backups - roughly 500 GB in size
3. Two monthly full backups (5 TB) kept at all times
4. Two semi-annual full backups (5 TB) kept at all times

• By totaling all of those backups, it appears that future proofing the solution, we'd be best off to have ~50 TB in storage if possible

Also, if we do in fact go the backup to disk route, how are taken offsite? How can I ensure the HDDs are not damaged while being transported? How would I go about swapping HDDs? Would I just setup the drives in a RAID array such that I can pull out the mirrored portions and take them offsite?

Thanks in advance!

Edit I feel like I should clarify that I'm looking for a hardware solution to be used to backup our data to, not a software solution. I guess I should have titled the post simply storage solution and not backup storage solution. I included backup in the title because I felt it was an important difference to note but it appears to have just added a layer of confusion.