It all depends on the equipment.
1 KW of signal can be made with a 1KW transmitter and an omni-directional antenna, or less signal and a more directional antenna.
A 1 KW transmitter may still require several KW of power to run it, though. As you get into much higher power output levels, though, you start paying lots more for cooling, maintenance, and other operational costs.
Our DTV transmitter costs $3500 a month for electricity.