[Zeke]

I think guides only is doable for the home mechanic with considerable skills and equipment. but that's only part of the story. Then the seats have to be cut and the valves dressed. A rebuilder will bead blast the heads and check for cracks. They will also be able to tell if any seats need to be replaced. Same with studs.

I think for all that you get for a grand is a good investment in that they are including the stems in the cost. New valves may run higher for the valves themselves, but the fitting is part of the base price.