Google now offers Cloud Storage Nearline (CSN) at $0.01 per GB per month.
Let’s say you have 1TB of data to store. That will cost $10 per month to store. Getting the data there is free if you have unlimited broadband, but getting it all back out (in the event of a disaster) costs $0.12 per GB ie $120.
A 1TB external drive is around £45 or $58 (quick prices from Amazon for USB 3.0 drives). CSN is not an alternative to local storage, but a backup; you will still have something like network attached storage preferably with RAID resilience to actually use the data day to day. The 1TB external drive would be your additional and preferably off-site backup. For the $120 per annum that CSN will cost you can buy two or three of these.
The advantage of the CSN solution is that it is off-site without the hassle of managing off-site drives and probably more secure (cloud hack risks vs chances of leaving a backup drive in a bus or taxi, or having it nabbed from a car, say). Your 1TB drive could go clunk, whereas Google will manage resilience.
If you consider the possibilities for automation, a cloud-based backup is more amenable to this, unless you have the luxury of a connection to some other office or datacentre.
Still, even at these low prices you are paying a premium versus a DIY solution. And let’s not forget performance; anyone still on ADSL or other asymmetric connections will struggle with large uploads (typically 1-2 Mb/s) while USB 3.0 is pretty fast (typically up to 100 Mb/s though theoretically it could be much faster). If you have the misfortune to have data that changes frequently – and a difficult case is the VHDs (Virtual Hard Drives) that back Virtual Machines – then cloud backup becomes difficult.