Wellllllllllllll, If you want an honest answer, I feel that since you can make sketches pretty quickly, like, within a few hours, you should lower your prices somewhat.

Don't get mad.. but.. maybe half it? xD

Cause sounds like you have more supply than demand, so lowering the prices would make economical sense!

That's until you get more popularz and then you can charge a premium for your art =p

makes sense