DIY machine work for heads??

Mean, if the performance really matters, I'd advise against doing anything yourself. Technology advances, and modern equipment is FAR superior to anything you might have, and most depend on good, straight guides. If you are doing a valve job with a stone and grinder, you're soing work that belongs on a flat head engine. Not a modern performance build. It costs me $75US per head to mill, but that's getting the ultra smooth surface finish, and flat within .001" accross the whole head. If it's a milling center like Rottler or Serdi or Sunnen, they do similar jobs and that is the going rate. If it's a small shop, with the large round wheel radial arm millers, that's why it's cheap, and they dont do any better job than the factory did, and many times, much worse.

as far as iron guides on the street.. I'm not sure where that comes from. Iron belongs in castings, bronze belongs in guides.