It can be done relatively cheap by reverse engineering a $15 power meter you get at home depot and combining with $10 worth of electronic parts and a $20 Arduino. Was a college project, and we blew up 5 meters before it worked. Working with 220V (or 110V) right next to 5V can be dangerous and not an easy "electronics problem".
it is my understanding that Wattvision taps the entire electrical system via the meter, not just a single outlet like a $15 "kill-a-watt" style power meter will.
That's true, but you need a combination of the two: both general and appliance-specific measurements. Like the post says: it's hard to figure out where power usage is coming from.
If you have more specific data and combine it with simple switching, you can achieve a much better awareness and higher savings. And the hardware doesn't have to be expensive as the "kill-a-watt" devices show.
