I went to a local machine shop that does flathead stuff, and mentioned I was looking for a magneto. The dude went into the back, grabbed one off the shelf, and let me have this old Vertex for $100... AND THERE'S NOTHING WRONG WITH IT!!! And I have a 318 Poly to put it on, too (it came off a 340-powered sprint car). Thought I'd gloat. ~Jason
$500 for a freshened up used Vertex with rare earth magnets from a reputable rebuilder is about average. That's for a chevy motor, though, not a flathead.
I paid a hell of a lot more for one for a flathead, that will look good on a poly. good score. Pays to ask!