The answer to the question of how much the nine books of Grave Robber's Chronicles cost at Xinhua Bookstore is uncertain because Grave Robber's Chronicles is a fictional novel series. The exact number of books is not clearly stated. If the bookstore chose to sell the entire novel, the price might be higher, and if the bookstore chose to sell a volume or a part of the novel, the price might be cheaper. Therefore, the exact price of the nine Grave Robber's Chronicles at Xinhua Bookstore depended on the bookstore's choice and the specific situation.