that doesn't look right.
you used MB where I think you meant GB (but that doesn't matter for comparison purposes)
It looks like you're using 1000 GB = 1 TB for your calc so I'll continue with that.
the LOT05 cartridge has a capacity of 1.5TB not 3
So the cost is $0.045 per GB
the LTO4 has a capacity of 800GB
So the cost is $0.031 per GB
The large tapes are more expensive than the sata drive but very close and certainly cheaper than I expected.
Of course they externalize the cost of the tape drives but the cost of that would depend on the size of your operation.
For a huge organization with thousands of tapes it is a small cost.
For a small org or an individual with say 30 tapes it is huge. To back up a 45TB collection (very large for an individual or small business) a $1600 (from newegg) tape drive would add $53 to every tape. So the real cost would be more like $0.081 per GB for the tapes.