Use of my images on their website

[LilmaK]

Hello I took some images at an event over the weekend and the organisers would like to use some of my images from the event exclusively on their website. I will be meeting with them in another few days to discuss these matters but I have I no clue as to how I should charge for exclusive use of my images. I don't mind doing it but I wish to make the best of this deal. Should I structure the price according to whether I have them credit the images with my signature or totally sell them? Advice please.
Thanks.