You'll find the Coffin Book through different catalogs and at different prices, most of them around $65 or more plus s/h.So, $25 at Mitchell's isn't a bad price.
Melissa was lucky to find it at $25 a couple of years ago.
I bought my copy in 1992 at Mitchell's and the price was $25 at that time. The Coffin Family Reunion was going on and Mitchell's was flooded with descendants purchasing the book. Mitchell's could probably have charged much more considering all the traffic they had in the store that week.
Dave Coffin mentioned several years ago that he bought up the few copies the Nantucket Historical Soc left because they told him it was going out of print.Dave told me he is planning to update the Coffin Family book but I have no idea as to when that will be in print.
I bought the Macy book, by Silvanus Macy, at Mitchell's at the same time, 1992, and it, too, was $25. It is now in Higginson's catalog for about $75 plus s/h.
I guess that demand has driven up the prices and I doubt that prices are going to come back down since genealogy has become such a big business.
A few years ago I contacted Mitchell's via email and ordered the book "Quaker Nantucket" from them. Melissa is correct that they are very easy to deal with and very helpful.