Machine shop prices vary wildly from place to place. So I would call a few and see what they would want to recondition a set. I can get it done for 225 per head here in West Michigan, I've seen people say as low as 75, and as high as 300 each. Of course part of the variable is what they consider fully reconditioned.
An authentic, new pair of GM Vortec head's are 632 at Jeg's right now, complete.