I checked Confucius' second-hand book network, and found that Yan Zhenqing's rubbings of Han Taizhong's Painting a Monument to the Oriental Doctor in the Qing Dynasty cost 3000 yuan, which is still relatively valuable compared with other engravings on this website.
Yan Zhenqing was a calligrapher in the Tang Dynasty. Gong Wenci is especially good at calligraphy, and he is called Yan Ti and Yan Liu with Liu Gongquan.