If you're going the made-in-China route with diamond plates, about $50 shipped can get you a whopping 12" circular diamond lapping disc on eBay. Makes lapping even large stones a cake walk, although from what I hear the old "float glass and loose grit" method is even faster and cheaper. $10 shipped glass "cutting board" off said big river site and a bag o' loose grit makes for a pretty cheap system, and from what I understand it takes a pretty long time before the glass goes out of true, especially if you manage the wear zones properly. When it eventually does, toss it in the recycling and get another cheap plate.