Personally, I think this kind of books can be bought online. Although there are many resources and discounts, it is not good to choose the consulting content. Instead, find a website that can be read and downloaded online.

In addition, if you still think that reading actual books is more suitable for learning than e-books, there is another way to help you: I don't know which city you are in, but you can go to your foreign languages college or the bookstore around the university. Generally, there are many people studying and assessing foreign languages in such places, and there are many language learning books provided by bookstores, and because the sales target is mainly students, there are usually many discounts!