Howdy
There are a couple of books available at Amazon right now for $299 or $300. You ain't going to find an original Merwin Hulbert anywhere for that price. I don't remember what I paid for my copy, probably a bit less than that, but it was expensive.
Look at it this way. It is not a great book. It is the only book on the subject, so pretty much all the collective knowledge comes from the Art Phelps book. The photos are good, and there is some good historical information. But I find that Phelps was quite biased, particularly the way he thought that the machining was so precise on a Merwin Hulbert that nobody else could have built them, which is ridiculous. If they had a mind to, Smith and Wesson could have built the Merwin Hulbert design, there is nothing in it more precise than anything Smith and Wesson was capable of doing. They simply choose not to. I strongly suspect the reason behind the unusual design of the MH was because of patent restrictions on some of the other better known designs of the time. S&W were very fierce about pursing patent violators.
And the S&W Top Break designs really were superior to the MH. As I believe I have said earlier, to unload and load a Smith all you had to do was break it open. All the cartridges would eject and the gun was open and ready to reload. With the MH design, once you have popped it open to empty it, you have to close the gun up and reload one at a time through a loading gate, not much different than a Colt. There was no way to load the MH while it was broken open.