Custom Card Art Pricing

Hey all, I was wondering what would be a fair price to put these at. I planned on just having these as a side thing to sell at a card show, but I’m unsure of what would be considered fair. A lot of creators price these simpler pieces at 10-15 USD (or so I’ve seen) and I know there’s a lot of room for improvement, but I just wanted a general idea.

I won’t be the one vendoring; my uncle will, and he said charging 10$ was too much. I figured maybe doing a gacha aspect would be cool too, but I’m not sure.