I agree, they should well be able to pay for the photo. However, if they wanted to be true asses about it, they could say "Give us the rights, or we will make you take the photo down from any other website." I have heard about that happening before.
As said above, I would find out what all of their intents are for the photo. If it is just for use on their website, I would charge a very nominal fee, and make sure they give me credit for the photo, but if they want to publish it on reports, hang it on the wall at HQ
, and distribute copies of it, they should be able to pay accordingly.