In any case, my charges are in line with current practices in the trade. You have two options here. First Use rights, and Full rights. First Use means you are only buying the right to use the art for a specific purpose. I retain copyright and any subsequent use you might want must be negotiated.
Full rights covers everything.
The art is yours exclusively, for any future uses that might occur to you. Rough sketches and ideas that are passed up in the process remain my property. All questions are fair game, and I'll do my best to make the process as painless and enjoyable as I can.