Actually every artist is underpriced since they can't make minimum wage off their art. Compare something like this which costs $100
http://www.deviantart.com/art/Battle...sion-349892037 and likely took 20 hours to sketch, ink, and color to someone flipping burgers for 20 hours at McDonalds. Which is more valuable? In our economy, they're equal.
Now some really good artists undersell themselves significantly, and these are usually talented college students who just want a reason to draw anyway. Hence why you have some amazing pieces going for the price of 2 beers at a restaurant; and people still say shit like "I can't afford that".