hehe..funny guy
look for one of these :
Newegg.ca - P3 Kill A Watt Electricity Load Meter and Monitor
quite precise for ones needs, unless you need a pro unit but that will be a couple hundred bucks more at least.
i plug mine in, take a reading at full occt and furmark, then slowly start oc'ing cpu/gpu and look at the power draw increase linearly with vcore/speed. hell it picks up an additional 120 mm fan(of the juicier variety) when added!
edit : how it helps you save money : say you have an older machine, wonder to keep it as internet browser or not. you discover it eats 100-200 watts for just sitting there. or you have two pcs, sell or trade the hungrier one.
or you plug it to your standby devices, like tv sound etc and you notice each one eating 10-20 watts or more by not doing anything. at this point you use your breakers more. hell, besides puter and fridge i leave nothing on unless needed.
edit 7 : holy crop i didnt know they had tehse too!! :
P3 Kill A Watt Power Strip - P3 P4320 - Electricity Usage Monitoring Power Strip Dytronix.com