My HDD has 150 GB used. It would take me 30 months to restore my drive from the cloud if I didn't exceed my 5 GB monthly cap. I haven't tried to figure out how much it would cost exceeding the cap, but I'm sure it's way more then the $150.00 or so I spent on an external drive two years ago.
I backup daily and make a complete image of my drive every two weeks. It would take about 20 to 30 minutes tops to be back up and running in the event I do something stupid to wreck my install. I have been stupid in the past, several times.