I also figure about $1/day added to my electricity bill for a tank heater (150 gal tank). I attached my tank heater to a thermo-box so it would only kick on in temperatures far below freezing (lower than 20°F). That was, of course, not enough to keep ice from building up, but only very little which I just broke in the morning and evenings if the horses didn't already do that. Now, I have a frost-free hydrant above the tank, it's easy to refill if I have to scoop ice out. The tank heater was only in use when it was so cold that ice yould build up too fast and too thick to break. I did try to leave part of the tank covered with ice for insulation, though. This saved somewhat electricity, but was, of course, more work-intensive.
I would rather spend $75 on insulating my tank, but my horses would chew on any exposed wood and play with styrofoam, so I couldn't figure out how to insulate. Also cleaning isn't really possible if I can not tip the tank over anymore.