Hi, about the sa-200's, I've had 3 machines all together, 1-300D which I sold, and the 2-sa's that I have now. What I always looked for when buying those welders was foremostly, a good generator that welds well with no serious electrical problems (inside the generator barrell) i.e steady arc characteristics and good output at all ranges of the selector switch. As for the engine, an engine can still run with a fair bit of problems, but it depends on your level of mechanical apptitude as to how much work you want to put into an engine.
the long and short of what I'm trying to say is that when I buy a machine, I weld with it with to make sure it has the arc characteristics that I like, make sure it has NO PROBLEM burning a real hot 3/16 7018 without sputtering (the engine I mean). As for the engine if I'm buying a machine that isnt a project I look for steady idle, not too much sputter when it idles down, good power under load, and no smoke out the exhaust or crankcase vent, it's okay if there's a little whisp of smoke out the crankcase vent as long as it's not really blue. Hopefully that kinda answers the question. Oh, about price it's all up to you, but the rest of the guys on here probably know better then I do, (I live in Alberta Canada and it seems like most of us pay more for the old 200's than our American counterparts, maybe it's the dollar, I dunno know??