Your quest to find a inexpensive water heater for the winter seems pretty easy to me. Grew up in Kansas and we had cold winters up there. Live in Dallas now since 1977 and it is much better here. Anyway a simple solution would be to buy a Kats engine oil heater  model #15200 [$11.99 at Northern Tool and Equipment] put it inside a copper tube and plug it into a timer.  Have to experiment with the on off time then insert it into the top of your bucket style waterer (wrapped in thermal wrap like for a home water heater) through a drilled hole and presto you're done. A more expensive way would be to buy a 35 dollar circulation type engine water heater and install it with a timer to run for 20 minutes every 2-3 hours or to keep the water warm but not let it freeze.  I have designed a simple method like this for a cattle water trough with the recirculating pump.

Loved the post on Julie's pegboard watering system.  I have an idea about winter time problems.  What about an heated horse bucket and an home made wooden lid with a hinge in the middle* to accommodate filling up the bucket as needed?

(*a two part, half circles lid with a hinge in the middle.  Hope that makes sense!)

I don't want to enter this into the contest since it isn't a "design" but more of an easy quick fix. I have a small urban flock and reused a small stick-on reptile heater that we had from a previous pet on your waterer. It keeps the water from freezing but doesn't really heat it.