Used Nelson model 730A-10WS aluminum and stainless-steel heated livestock waterers; these waterers have 13" bowls and 250 watt heaters. $325 each; I am willing to entertain an in-person cash offer for the 7 waterers remaining for sale! If you see this listing the waterers are still available, cash only, no trades, calls only -- texts and emails ignored and blocked.
These waterers were installed in a horse barn in 2001 and all were working when last used in 2008. These waterers have been mounted inside horse stalls and kept out of the elements since new. My asking price takes into consideration that some waterers may need replacement parts to put back into service (all parts still available through manufacturer).
Parts for these waterers are still widely available:
https://www.nelsonmfg.com/parts/product-category/730-8w-730-10w-waterers/