How much electricity will be Used?

[TheAskerer]

I plan on building a gaming computer with a 650 watt power supply.

How much money would this have me spend per month?

 

[USAFRet]

How long is a piece of string?

That depends on many, many factors.
How much will you use it, at what performance level, how much will it be idle, what do you pay for power, at what times of day...

Anything from $0 to $100/month.

 

[ddpruitt]

How much food will I need for a 200 sq foot kitchen.

Same question, can't be answered.

 

[clutchc]

The PC system will only use as much power as it needs. Never the full 650W your particular PSU can provide. At idle, most gaming quality PCs will use the same amount of power as the average 100W - 150W incandescent bulb. Maxed out... well, it will depend on the components drawing power; mainly the graphics card. If you want to check your system for power usage, pick up an inexpensive Kill-A-Watt meter and set it to monitor the usage by entering the rate for your area.
http://www.amazon.com/P3-International-P4400-Electricity-Monitor/dp/B00009MDBU/ref=sr_1_1?s=hi&ie=UTF8&qid=1370915306&sr=1-1&keywords=Kill+A+Watt

Electric rates vary across the nation, and they are often calculated differently for different electric service companies. A really rough rule of thumb is to figure an average of 10 - 15 cents per killowatt hour. But that's really rough. Your electric bill should have a breakdown of the rates and how they are figured.

But with your 650W PSU, you will never use more than 650 watt hours of energy.