Pricing pictures for Tourism Magazine

[evader]

My sister and her family live in a "touristy" town...ski hills, waterfront, etc. and when I'm up there visiting I always set aside some time for myself to go out with my camera.
About a week ago my sister and her friend (who runs the tourist association up there) were hanging out and my sister showed her some of the pictures I've taken when I've been up there.
Friend said she was impressed and might be interested in using some of the pictures in their upcoming "Visitors Guide".
Couple of days ago I received an email from the lady telling me who she was and what she did and she asked if I had anymore pictures she could look at.
I sent her a link to my online gallery (all images have a copyright symbol on them) and she emailed back and asked me for a price per picture and said there were 16 images she would like to use.
She then proceeded to tell me they are a non-profit organization and they "usually offer photo credit and a free membership to the tourist association for use of pictures".
My sister says not to buy the "we are non-profit and have no money" because she knows for a fact they just got a big fat grant. Also, I would expect photo credit anyways and a membership to the tourist association would be no good for me as I don't even live up there.

Anyways, I'm by no means a professional photographer and 6 months ago I probably would have said..."ok...you can have them all if you want them"...but since I've been a member here at DPS I've read a lot about the importance getting fair market value for your images.

So, I'm asking if anyone has any suggestions as to how much to charge per picture for something like this.
Thanks