My ducks do just fine with their kiddie pool made of rigid plastic I got for $25. 4ft diameter 10" high. I would look around and see if anyone is throwing out stock tank/tubaware/old fridge/anything like that. A mechanic might throw away an empty 55gal barrel, but you'd have to build it stand,clean it, seal the holes, and cut an opening in the side to make a tank of it.