Selling Models/Skins - Decent Pricing?

If someone were to do some contract work and sell models/skins, what would be fair pricing for these? Is there such a thing as any industry norms here?

I have been looking around, and it is hard to know what should be charged for these types of things. Anyone have any input/experience for things like:

Player Model/Skin
Animated Player Model With Skin
Player Skin

Thanks!