Plasma TVs do not use that much power. People react to the power consumption spec on the spec sheet or the back, but that is the MAXIMUM power consumption of the plasma at peak brightness. The power consumption varies dynamically with the brightness of screen with peak power for all white scenes. But since most of us have the brightness level set to somewhere around half, the TV is not going to hit the peak power consumption on the label. For example, my Panasonic TH-42PH7UY varies between 90 and around 220-230 Watts in power, but averages around 140 Watts (measured several times over a 4 hour period). The maximum power on the spec sheet for my model is 357 Watts.
In normal use, the power consumption of the plasma runs somewhere around 40 to 50% of the maximum power on the spec sheet. The TH-50PH9UK has a max spec power of 460 Watts, so you are probably running around ~ 190 Watts when it is on. Even if you left on 8 hours a day, that is 1.5 kWH a day or 45 kWH a month. Switching four 75 Watt incandescent bulbs with four CFLs will make up the difference and likely will more than way make up the difference between the TH-50PDH9UK and whatever TV you had before.
The myth of high power consumption for plasmas goes back to the early generation models that were indeed major power hogs and generated a lot of heat. Some 3 or 4 generations back, Panasonic and Pioneer made major strides in reducing the power consumption of plasmas so they are no longer the hogs they once were.
My Motorola HD-DVR consumes more power over the course of a month than my Panasonic 42" plasma. The DVR is always on, even when it is "off", running around 42 Watts when it is off (although I do need to measure this for my newer Verizon Fios Motorola 6412 DVR). That works out to around 1 kWH a day.
I agree with the other posts. You are in a new place with a different heating & cooling system. Do you have gas heat or a heat pump? Electric or gas water heater? More square footage or less efficient home? Did you move your refrigerator or use the one that came with the house? If the new place came with an older fridge, that could be one source of increased power consumption. Refrigerators have made major strides over the past 10 to 20 years in reducing power consumption and improving efficiency to the point where it may be worthwhile replacing that 20 year fridge in the basement with a new basic unit. Replacing burned out incandescent bulbs with CFLs is the easiest way and has the fastest return in reducing your lighting costs.
There is a very handy device called the Kill-A-Watt which measures power consumption of any plug-in device. Very useful to measure the power consumption of your fridge, DVR, TV, receiver, computer, the countless wall warts that we accumulate like barnacles these days. A google search for "Kill-A-Watt" will turn up a bunch of on-line dealers.