$60 to $200 for a plate to flatten sharpening stones? Ridiculous. Y'all have to be kidding.
Just toss a dry sheet of 25-cent, 80-grit wet-or-dry paper on the ground jointer table and have at it. It'll make short work of sandstone.
““Perhaps then, you will say, ‘But where can one have a boat like that built today?’ And I will tell you that there are still some honest men who can sharpen a saw, plane, or adze...men (who) live and work in out of the way places, but that is lucky, for they can acquire materials for one third of city prices. Best, some of these gentlemen’s boatshops are in places where nothing but the occasional honk of a wild goose will distract them from their work.” -- L Francis Herreshoff