New York City resident here and it works out to about $0.28/kWh. Studio apartment with a MacPro and DroboPro with eight drives and on a typical month (with the MacPro only on while in use), the bill is $90. In the summer with the air conditioning, it's $200-$250. For a 300 square foot apartment.

They're called Enterprise grade drives. They usually cost 2X more than the consumer level drives.