This is one of the most expensive books in the world, and it is available to buy: „History of the Expedition under the command of Captains Lewis and Clark, to the Sources of the Missouri, thence across the Rocky Mountains and Down the River Columbia to the Pacific Ocean. Performed During the Years 1804-5-6.”
It is a narrative of the famous American land expedition. 1,417 copies were printed in 1814. Approximately 23 copies remain extant with very few in private hands. The journals originally were paperbound, with the plain cardboard front cover.
The price: 350 000 USD. It can be bought at Powell’s City of Books, the largest used and new bookstore in the world, occupying an entire city block and housing approximately one million books, located in Portland, USA
You can read more about this gem here and here.