question about getting paid for photo gig

I took a bunch of photos for an organization. They were billed and the job was paid for. Two years later they now have decided they want to make a book and two handfuls of the photos wlll be included. Being "green" I didn't realize the work involved in this process--the emails, (around 40) the editing, looking for other photos from the shoot that might work for what they are looking for etc etc.

I was only paid for the original photo shoot two years ago. I knew that they could use these photos for any purpose they wanted in the future. However, I now feel like I am working for free and don't know how to bring up the subject. Can someone help?