I prefer not to spend money when I feel that I can get exactly the same thing for a great deal less or even nothing at all. And then, as a desperate bookworm I feel that I have a little knowledge about finding books cheaply; and I flatter myself that I could recommend to you where to find some books as well.
Libraries of course come first. It is not so very hard to find what you want in libraries, if you know what to look for- and perhaps even easier if you don’t know what to look for. I just wander backwards, and browse for the battered covers, or the Great Illustrated Classics series, or architectural pictures.
Another thing to keep in mind in libraries is a list of the titles you want. If they don’t have them you can request them; and pray the library at the other end doesn’t lose your book (it happens).
The best resource for cheap books to own is to frequent your local used bookstore. I love used books, as they have so much charm and character- I once found a book in one store, a book meant for the kind of reader that smells their books (the fly-leaf said it, not me). But I have turned aside from my point. If it’s a series you are looking for, say, Agatha Christie, that isn’t in chronological order, I recommend that you look at all the books and find the very cheapest ones. And look at the different editions of the book in question, for one may be a dollar or two less then another.
Surprisingly, e-reading is the cheapest way to go. There is no physical volume, of course, which disappoints me, and the books have no character. But the content is the same, and that is what counts, after all.
On e-readers out-of-print books are the way to go. There are dozens- hundreds- thousands-, and there are enough and plenty to satisfy most tastes. History books, for instance, and a few novels, and old things such as Plato’s work, etc., are all free. Plenty of good poetry, too.
Well, I hope this is enough to inspire you to read some books either very cheaply or for free. Enjoy!