I'm wondering if they use in-house artists who get paid a salary or if they buy something from someone then add an upcharge and what that upcharge percentage rate is. I do custom work for Home Expo (custom high-end division of Home Depot) and they add a 33% upcharge to my price. But this is more of a one-off thing since I can't sell stained glass windows like this. Since they'll be licensing images they'll make their profits back in mass-market selling so I'd say go high and haggle down as needed.