Most of the analog security cameras I use only require 0.5 to 1 amp at 12V DC. Some with a PTZ (pan, tilt, zoom) feature may need 2 amps. The amount they use also varies from day to night because of the infrared LEDs used for the night vision. That comes to an range of 6 to 24 watts. Given that there will be some losses in the power supply unit lets say 8 to 32 watts. Even at the high end a kilowatt hour of power, the basic unit for billing, should operate the camera for 1000 / 32 or about 31 hours. Given the average cost of power that means about 9 to 15 cents per day of use. Multiply by the number of cameras in use and add about another 100 to 150 watts for a DVR and a TV monitor and you can do the extra math.

I should add that most of the common IP cameras available, be they ethernet or WiFi, should have similar values.