At my school we have somehow ended up with an over-abundance of water heaters. I have 4 barely used 1000 watt tank de-icers. These have a wire cage, so they can be used in metal or plastic tubs. Shipping is probably going to be $10-20. These don't quite keep up when they are in a 100 gallon tank, and the weather is -20 for a couple days, but if you live somewhere slightly warmer than MN, or don't mind breaking a little ice they'll do fine.
Would love to see them go to a great farm or school!