I've been recently contacted by a company to sell them two of my photos. So far so good, no problems at all, I've consulted the stock photo price link that was given here on some other topic and we have reached an agreement on the fee.
The material they will publish and for what I have sold the photos is a paper newsletter and now they also want to publish some of the contents on their website and are asking me how much will I charge for that usage. The question is that I don't have the faintest idea of how much should I charge, if anything. My initial idea was to let them use it for free (as they already paid the paper edition) if they only reproduce the newsletter on a PDF. To me that is the same material, so no extra fee should be charged. But if they want to make something different, like have a webpage with the photos and text, custom made for the internet, how can I measure the prices, and should I or shouldn't I charge anything else ?
I really need some help here
Thank you all in anticipation