The most comprehensive English textbook should be the Shanghai International Studies University Bookstore on Dalian West Road at the entrance of Shanghai International Studies University. Generally, new books are not discounted, but there is a discount counter.
The university bookstore next to Fudan also sells discounted English books, at the Wudong intersection of Guoding Road.
There is a 20% discount on new books and magazines in the Confucian Temple, and a minimum of 30% discount on big books such as martial arts novels, as well as old books.
There is a book wholesale market at No.8 Memorial Road, which was previously moved from Qianhu Road in Wujiaochang. It's famous and the discount is beyond your imagination. I bought a complete set of China history, but it was only 1.5 discount. A few thousand yuan set of books in the bookstore outside will not be more than 30% off here, and English textbooks will not feel anything. Only four or five companies specialize in foreign languages, and all of them are basically 20% off.