What are your rates?

I got an e-mail today from the photo editor of a (non-biology) textbook asking if I had some photographs of specific biology content she needed. Since I had some photographs that at least somewhat fit her needs, I e-mailed her a quickly made contact sheet and said to let me know if they would work. No fees or payment were mentioned, and I figured what I had probably wouldn't work anyway.

Less than an hour later I got a response implying that some of my pictures might work, along with more details on what she needed (including asking about the possibility of commissioning some custom-shot photos). What's stumped me about the e-mail, however, was her final question asking what rates I charged for the use of my images.

Um, yeah ... let me just open up the ol' rate sheet sitting on my desk here and I'll let you know how much it'll cost ya.

Charge? Presumably I should respond with some sane estimate of what I think these photographs are worth (they're not unique), but in all honesty I have no idea what going rates for scientific photography are (either pre-done or custom).

I've looked a bit online for advice, but most of what I've found is just suggestions on how to get your work in the likes of National Geographic, which is decidedly unhelpful for this situation.

I'll keep looking, but any advice from those who know more would be nice.

Note: For those who are curious, none of the photos this editor is interested in are from my blog, and I do not believe that this person knows of my blogging. There are times when it's nice to blog anonymously.