Cost to leave your Television on all day for 24 hours will depend on the wattage of the TV you intend to leave on all day.
My TV uses 50 watts of electricity so if I leave the 50 watt TV on for 24 hours it will use 1,200 watts per 24 hours.
Assuming 31 days in the month 1,200 watts per day times 31 days equals 37200 watts per month. My KWH cost is 8 cents per KWH before all the other taxes so to leave the TV on all day would cost me roughly $3.00 per month.