Why are Gu's books so expensive?

Gu's books are so expensive because of their high reference value and high status. Gu Hongyi, a researcher at the Institute of Ancient Books of East China Normal University, is the executive director and secretary-general of China Historical Literature Research Association of China Institute of Ancient Books. His works are of great value to China's academic research field. He won the second prize of the 33rd National Excellent Ancient Books (20 17) and was regarded as a milestone of China's classical literature.