I used a 250 degree. I was doing it by the book for the first week and then I saw my neighbor's hen with her brood following on a 75 degree day. They were 5 days old and doing fine. But I realized that if they started to get cold Mom would call them and they would go back to the nest and she would warm them up. After that I kept it warm but it allowed me to be confident enough to take them outside.
I ran the lamp for 5 weeks and then went to just a normal light during the day and darkness at night. When my electric bill came in I was a bit surprised to see that it was over $30 higher for the first 4 weeks I ran the light. The light for the chicks was the only new thing. I guess a buck a day is ok.
Good luck with your chicks!