I suspect that many on here will know of Abebooks but a little reminder or info for newbies may be worth while. They have sites in the UK & US, plus many more, you can check whether books are available along with prices and postage, order through them and the book seller will send your order direct to you. Some rare books are liable to be expensive and postage from the other end of the world can be more than you might imagine. However I have in recent weeks picked up a couple at very reasonable prices, including one of Graham Goodchilds' model books, for £3.50 which included postage and packing, looks almost to have never been opened. Worth a look for that book you always meant to buy.
Syd J
UK site: AbeBooks.co.uk