I am using tape for archiving my data and the break-even point with hard disks, the last time when I have checked, perhaps one year ago, was somewhere between 200 TB and 300 TB of stored data, after buying a tape drive for about $3000.
For larger amounts of data, the money savings vs. HDDs increase quickly.
The break-even point vs. HDDs is lower for long-term archiving than for short-term backups, because the lifetime of tapes is much longer (it is limited not by the degradation of the tapes but only by the risk that compatible tape drives might become hard to obtain), so you need multiple HDDs to store data for the lifetime of a single tape.
For larger amounts of data, the money savings vs. HDDs increase quickly.
The break-even point vs. HDDs is lower for long-term archiving than for short-term backups, because the lifetime of tapes is much longer (it is limited not by the degradation of the tapes but only by the risk that compatible tape drives might become hard to obtain), so you need multiple HDDs to store data for the lifetime of a single tape.