Regardless, there is a cost associated with having that harddrive (on or not) sitting in a server in a datacenter with air conditioning and resilient power. My point was not accurate to the exact operating cost per drive, but if you want that, here it is:

1) 2.5kWh per month of drive-on power. Datacenter grade power: 30-40c/kWh normalized =~ $1.00 in power per drive. 2) 60 drives per 4U space. 10 storage pods per 1 rack. 600 drives per rack. full rack in a colocation facility: $250-$500 =~ $0.40-0.80 in physical space.

Total cost per year to keep that drive up is, very ballpark, $16-22. The cost of running the drive is minimal vs the initial cost of $500 for the drive and storage server/rack/installation/network equipment etc. Network costs to transfer data from/to that drive are obviously nontrivial but again, the majority of the hurdle is outlay for capital.