Wow, your electric rates must be high! A 75 watt bulb here (24/7) would be about $7.29/month and our rate is around 13.5 cents a kilowatt. That is about 3 dozen eggs a month and I get around 20 dozen from 12 girls, so still would be OK. My 40 watt bulb on 5 hours a day costs about .81 a month. A 40 watt bulb is enough for an 8 by 8 coop. Why would you light 24/7?
Timers are inexpensive and work great but maybe some folks haven't shopped for one and don't know. My light is on 3-6:30 until the days lengthen enough to back it down. 3.5 hours per day with 40W isn't much at all.