I own a plasma, it uses more energy than an LCD set.
However, I doubt you will notice any huge increase in your bills because of it.
LCDs don't use that much power, so even if plasma uses 50 percent more or 75 percent more, it's that much more of an amount that isn't a huge draw.
So, hit google, and look for estimated cost of plasma (42 inch, 50 inch etc) some sites that review plasma give these figures.
http://www.energyrace.com/commentary/beware_the_plasma_tv_electricity_bill/
In this article, the author claims that going from a 28 inch TV (no such thing in the US, maybe a 27?) to a 60 inch plasma will cost an extra 100 dollars in electricity in one year. That's an extra $8.33 a month.
If they were trying to be dramatic, it didn't work. 8 bucks extra a month for a 60 inch plasma? That's nothing, you can't buy a new release DVD with that. That's one trip to McDonalds. And that's for a 60 incher.
If you spring for a 42 or 50 inch plasma, it's slightly less I'm sure.
So what do you gain over LCD?
NO lag time like LCD. Doesn't sound like a big deal on the surface, but LCD resolution can drop to half where motion is concerned. LCD fanatics don't like to talk about it, or don't know about it. LCD max resolution is only good for static images.
NO shift in image quality, light output or color shift when you aren't sitting right in front of the screen, you also get a wider color gamut and in most cases better, deeper blacks. Plasma is also cheaper per inch than LCD.
hope this helps.