Since they didn't hire a real photographer (they just asked you on the spot) they probably don't have an idea themselves of what to charge. So, within the boundaries of not charging a gross amount or a puny amount, you can charge whatever you want. I'd charge $150-200. I don't know if that's what you were looking for, but today there is so much predatory pricing in the photography business nobody knows what to charge any more [8o|]