Hi there! $15 covers most commissions, ones like the two examples I posted (can have wings and/or horns like the ones above) and of course any colors/designs needed on the pony. They will also be sealed to protect their paint job. I would just charge extra if someone needed big, fancier wings or like a sculpey mermaid tail or something like that. Is that what you meant?
Oh, and shipping is not much for these guys since they are so small, but those with sculpey parts will have to be shipped in a box to avoid breakage in the mail. Still, it should only run about $2 in a box in the US.