May I introduce three of the many Tolkien & Tolkien-related books I own, maybe you would like to purchase them for your own collection.
They are surely a wonderful addition to every book collection.
The first one is called "The Hobbit companion". It was written by David Day and illustrated by Lidia Postma. A wonderful small book (90 pages) for everyone who wants to know all there is to know about Hobbits and their culture, all in one small pocket-size book. I found this little treasure on a convention market, the price is £4.99.
The next book I'd love to recommend is "The Lord of the Rings Scetchbook" by no other than Alan Lee himself. A beautiful compilation of his artwork with explaining text. 192 pages but I do not know the official price for this book. I bought it for £50 at a convention (price translated from € price).
And the third one is "The international relations of Middle-earth", a fine book for all who want to compare our political and international structures to those of Middle-earth.
Written by Abigail E. Ruana and Patrick James. £10 for 215 pages of interesting facts. If there are hardcovers, maybe you have to pay more, I bought a paperback version, not sure there is an option.