Yeah, artwork is surprisingly expensive if it's customized. Obviously it's possible to get really cheap artwork, but we've found that quality and reliability are worth paying for. We also allow every winner to iterate the design a few times to get what they want.
What is a code combat wizard and why would we be interested in having one? It sounds like some sort of in-game reward or skin for your avatar, and giving it an imputed value of $500 is pretty optimistic. Has anyone ever paid $500 in cash for a CodeCombat Wizard? NB that the value delivered is not related to the cost for you to produce it.
You might consider putting in an explanation of what these things are and why they are worth more than the services you're giving away with a link on the text, and putting them at the end of the list, because for most people not familiar with your game the value for an in-game character or avatar will hover just above $0.
