After a cursory search on Ebay it looks like they actually sell for between $25 and $50. Some price them higher but they evidently don't sell for more. Condition and quality of the stamping (detail) seem to dictate how much they sell for.
I have found a few through the years but they were too corroded for my taste and I didn't save them. They are most likely from the golden years of fruit jar canning, about TOC but I could never ascertain exactly what dates.