This is the same as what you see on places like Ebay. Do a search for a certain train car and you will find a whole range of prices.
Doing a search for a certain book, you can come up a number of book sellers all with a range of prices from very reasonable to stratospheric. Use different sources such as Amazon, Abebooks or Alibris and you can more often than not find what you are looking for at a price you can afford. Book condition will be a factor in price as will how rare the book might be and how much the seller thinks they can skin you for.
One reason that I don't like buying "sight unseen" is that the book (or any item for that matter) might not come up to your expectations. I have bought many a book like that and thankfully have been able to resell them without a loss. Be careful, some of those books, many by well known authors, that you think you need are nothing more than fluff jobs!!!
