Here's a link to give an idea on how much power a plasma, standard backlit LCD, and LED-backlit LCD consume.
The chart: HDTV power consumption compared - CNET Reviews
Plasmas have great PQ, but the power consumption, heat dissipation, and the limited availability of 1080p models were a turn-off. The 42" LG LED TV I have is only using up about 45W with the Eco mode set to minimum, and about 30-35W when set to maximum. By comparison, a plasma display of the same size can consume anywhere between 180-280W. Not to mention that the extra heat generated would mean your A/C (if you use one) will have to work a bit harder to cool the room, adding to the overall electricity cost.
Always look at the total cost of ownership (TCO) rather than just the up-front purchase price.