Considering that there are ca. 1.2 billion potential internet users in China (just kidding!), the sales are rather low.
I sold sub.cn two years ago for only $ 140. It was a slight loss, but I wanted to get rid of it. Before that, I only had very few low offers, not reaching $ 100 each.
I don't think N*.cn domains are widely used in China. They rather prefer IDNs in chinese characters, and there are already chinese TLDs (one official, and others for China only).