Every year, the Stewardship and Mission Committee at my dear seminary has a book sale. Thousands upon thousands of books are donated by students, faculty, alumni, friends of the seminary, widows/widowers of alumni. All of the books are then sorted and sold for very low prices to the Princeton community. The proceeds go to seminaries in developing countries and some of the books that are left over are donated to them. Because so many books are donated, it takes a multitude of people to sort and box them. All of the work is done on a volunteer basis, but for each hour one works one gets to choose a single hardcover or a couple paperbacks.
Many of the books donated are less than desirable; similar to the junk that people would take to the local Salvation Army store or Good Will. But, while sorting, it becomes easier to find the gems amidst the piles of rubble that should never have been printed in the first place (e.g. multiple copies of The Purpose Driven Life). Tonight, after I had already left, someone discovered a Greek textbook and a preaching textbook. Jordan was there and later told me of the discoveries. So, at the low low price of 1 hour of sorting, I've acquired two textbooks that probably would have cost nearly $50. Now that's what I call a good trade.