The price difference lies in different publishers, different proofreaders, different versions of A Dream of Red Mansions, and sometimes in whether there are famous inscriptions in the book, whether there are Xiu Xiang treasures and so on.
Difference between publishing houses: People's Literature Publishing House and Shanghai Ancient Books Publishing House. These publishing houses use paper, and the strictness of proofreading edition is much better than that of publishing houses. The price is more expensive.
Proofreaders are different: sometimes some publishing societies invite some famous red scholars to proofread, thus raising prices through celebrity effect.
Different versions of a dream of red mansions: There are many versions of a dream of red mansions, and the popular version is Cheng Gaoben, which is the most common version. For example, People's Literature Publishing House once published a fat review version of A Dream of Red Mansions, and the price was much higher than the ordinary version.
Whether there are famous inscriptions in the book, whether there are Xiu Xiang's works, etc.: whether it is hardcover or not depends on your own preferences