>>8499326He's saying they go for cheap because they're older figures with outdated engineering. Shadow Moon, along with the vast majority of Showa Kamen Rider Figuarts were released before the line saw a large upgrade in sculpt accuracy as far as proportions and and detail go, as well as major changes to the articulation schemes.
Souchaku Henshin meanwhile was the line that predated and eventually became SH Figuarts. They were in high demand back in the day, but not so much now.