(Odograph - n. an instrument recording distance traveled, especially by a pedestrian.)
I have a Kill-A-Watt monitor that I like way too much. It was a lot of fun for forty dollars or whatever.
The easiest thing to do with the monitor is plug it into something like a refrigerator and let it run for a few days. It will tell you the number of kilowatt hours (kWh) consumed during that time (and the time in hours and minutes).
This calculator extends those kWh (and times) to month and year, and works out the cost for that energy.
please enter some values and press "(re)calculate"