The price of rubbings of inscriptions in and after the Song Dynasty is not high, because there is printing in the Song Dynasty, so the most precious inscriptions are the times before the Tang Dynasty. Su Shi's works are in Xi 'an Beilin Museum, about 1000. Most of his inscriptions were carved in the Ming and Qing Dynasties. Many of his works were destroyed by Wutai Poetry Case and Yuan You Party Case in Song Dynasty, so they were later engraved with his ink in Ming and Qing Dynasties.
So the price is lower.