$250 American. Each. Because you're a beginner. Once your reputation has developed, you can get $500 - $750, I would imagine.

This is a little more than I've seen web graphics rights sold for, and less than reproduction rights to physical artwork. It isn't just an arbitrary amount.

These are beautiful kits, BTW. I'm sure you could sell them yourself and make more in the long run, but since these are your first kits, the exposure that the big store will give you might make your own site hits climb and you could sell future kits in your store more easily.