Calling professional and hobby artists:

I’m commissioning a small bit of line art from a friend for non-commercial use and want to make sure that they are fairly compensated for it. My friend has a habit of trying to offer “mate rates” and under-valuing their work.

For something like voice over, I can refer to SAG rates sheet to quantify that I can’t afford projects with voice acting. Are there any similar things for line art/simple drawings that I can refer to, or at least guidelines that people can offer, so that I can force them to take fair pay?

Context: The drawing in question is a medium-sized cartoon/fan-art of an existing character. It is limited to 3 colors so that it can be used to create stencils to airbrush onto a DIY greeting card.