I've recently done a shoot for a customer where the contract stated they would get "web ready" digital versions of the photos (max dimension 1024px), as well as the ability to order prints. The customer is very happy with the images, and I'll be giving them a ZIP file of the 'web ready' images.
They've come back and asked for 'high resolution, non watermarked' versions of some of the pics (I said we could talk about that afterwards), and they are okay paying for it (I made it clear up front that photographers generally don't provide digital high resolution versions of their shots).
My question right now is how much to charge for each of those high resolution images. They've already paid for the shoot and the postprocessing work, and the payment was fine. I hope to get a few hundred more from prints, but I don't want to be a jerk about asking for $75 per 5000px image. I'm thinking $20 per image - which is the max I'd make on a digital print of that pic anyway.