There are some photography books that are so unobtainable or expensive but I still hang onto the hope that I might come across them in some dusty bookshop's cellar one day. This is number one in an ongoing series of books i'd love to own (but unlikely I won't).
Twentysix Gasoline Stations was Ed Ruscha's first book and is, as you can guess from the title, photographs of gas stations. Specifically ones to found along Route 66. The book contains no descriptive text other than the station's brand name and location.
The original book was published in 1963 and was limited to a print run of 400 copies. Two other prin runs followed; one of 500 copies in 1967 and another of 3,000 copies in 1969.
If you want a first edition then you're looking at over £8,000.
(If you'd like to aim for something cheaper than you can get - at the time of typing - a copy of 'Thirtyfour Parking Lots' for £6-700).