Why are the special 57 Huangshan stamps so expensive?

Because it is the first set of famous Chinese mountain stamps since the founding of New China.

The 57 "Huangshan Scenery" special stamps issued on October 15, 1963 are the first set of famous Chinese mountain stamps since the founding of the People's Republic of China.

Special 57 "Huangshan Scenery" belongs to collectibles and stamps. To showcase the wonders of Huangshan Mountain, the Ministry of Posts and Telecommunications issued this set of special stamps "Huangshan Scenery". The 16 pictures are all representative scenic spots in Huangshan, and were designed based on some of the photographic works in the "Huangshan Landscape Photography Exhibition" held by the Chinese Photographers Association in Beijing in 1962.