Somebody wrote,

You could try posting or looking on Craigslist. I'd bet you can find
someone local to grind it for a lot less than the $500 the one guy
wanted. Of course when dealing with someone from CL or the like,
whether they have insurance an such can be an issue.
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If you do post on Craigslist, (a god idea, in my opinion), include a photo
of the stump with a ruler or something else in the photo to give the viewer
an idea of the size of the stump.