Art pricing is actually quite simple.
There are three ways to judge how you should price your art: Quality, Complexity and History.
Quality - Get some opinions of your artwork before you start selling it to see what people think of it. If people love it enough, you can probably charge a higher price for your artwork, so long as you can provide some just for show.
Complexity - No matter how good of a red cube someone might draw, I'm not paying $20 for a single red cube. The more complex your artwork becomes (e.g More colours, more details, etc.) the more you should charge for it, simply because it would take more time.
History - People are more willing to pay higher for an artist they can rely on. If you've got a solid backing behind you, raising the price a little to make more of a living off of it shouldn't be too much of a problem.
I recommend going to to places such as Furaffinity where there are plenty of people who sell their artwork and see what prices there are. It'll come down to experience and experimentation, but here is a generally good rule-of-thumb; People pay more for cheaper things