It depends on the level of work. Give the skateboarder options in quality because some are just looking for something to just cover ugly bland, others are looking for art. But most of the people looking to just have something will go buy stickers.
You also have to design your own art, you can't spoof or base any of it off of something readily available.
Depending on how skilled you are, start at $50 for labor and materials. When you acquire new designs and skill, start ranging your prices from $50 + depending on the difficulty of your design.