These books are all hundreds of pages thick.

There are also cheaper ones, maybe about twenty or thirty pounds, just because the books are thinner.

Second-hand books are basically luck, but on average they cost at least half the price of new books.

If you are lucky, you may come across very cheap second-hand books.

In fact, if the books in the library are not very important or scarce, there is no great need to buy them. I only buy two or three books a year and borrow the rest from the library. After all, buying books costs money.