The best thing to do is to look for a shop that knows these cylinder heads. Looks like you've done that. I asked a local shop about the work involved and cost estimates and the guy seemed knowledgeable.
You didn't mention cleaning the head, checking for cracks and surfacing the mating surface if necessary. This guy quoted something like $330 for all that and lapping the valves, and checking what valve and guide work is necessary.
He said that later M103 valve guides are much better than those on early M103s. He said that he measures each valve and guide an replaces only what is out of spec. He doesn't just replace all the guides. I'd almost prefer if he'd replace everything, but again, he seems to know what he's talking about. Cost is determined by the number of pieces that need replacing, and it doesn't sound marginal.
He said that it's easy to damage the head by not following the cam bolt tightening/loosening sequence and observing the appropriate torque. For an extra ~$60, he takes care of removing and reinstalling the cam and swallows the cost of damage. And he inspects the cam and followers if you bring them.
I estimated the total to be just under $700 if all the guides but none of the valves need replacement. I'd be curious to hear if this is normal or high. This shop has a reputation of being pricey, but they also have a reputation for getting it right the first time.
I wonder what kind of controversy the practice of not replacing all the guides will start in this forum.