I was curious, so I ran everything off a single power strip and connected it to my kill-a-watt device.
At idle it was about 100 watts and when scanning all of the drives it was at about 150 watts.
With a block every 4 minutes and mining taking about 1:30 to scan the disks we can assume that we are using about 120 watts on average.
If you take this and multiply it by 24 (hours) and 30 (days) and divide it by 1000 (kilowatts), you get 86.4 kilowatts per month. My rate is 7 cents per kWh so I pay roughly 6 dollars per month for my mining rig.
Not bad at all.
Hope this helps someone,