I'm cross-posting this - I noticed the first thread I posted it on was in an Urban forum (I'd found that by searching for re-purposing threads). This is more relevant to small farms, I believe.

Repurposing a bucket, heating element, toilet-tank water valve, and other parts to make a high-output self-refilling humidifier (useful for crop storage rooms, etc) - pictures, description, and a wiring schematic are provided. Also, he's listed where he obtained the parts from.

On Farm Hack: http://farmhack.net/tools/auto-fill-high-output-temperature-controlled-humidifier

The designer/builder used new parts and the cost is reported as $155, but he points out cost could be save by salvaging some (most) of the parts.