A First. How Much To Charge?

A web development and design firm has asked to purchase the right to use one of my photographs commercially. This is the photo in question:

Stephen Birch Aquarium, La Jolla

I took it at the Stephen Birch Aquarium in La Jolla. This is flattering. I’ve never had anyone want to buy one of my photos. Although, I have had my photos used in several online publications including, most notably, The Wall Street Journal. I license all my images under Creative Commons, Attribution-Share-alike.

I suppose I should donate the money to the aquarium. I have no idea how much to charge. Thoughts? I do not know how they’ll be using the image. I’ve asked for clarification.