Update the description of your tool to be clear about what resources will be used.
I have more than 28 GB of original-size photos. I have no idea how many GB of info that will translate to if I go with "large" size. I have a limited Internet connection (I live in Africa right now), so I was hoping that perhaps the tool would work entirely on-line, e.g., not use my bandwidth or computer.
I also like the idea of including an "analysis" step where there is a scan of my photos and an estimate provided of how much info and how much time.
Finally, I agree that it should be ok to ask to get paid for this. The folks at "Mover" use a $1/GB model for moving files and I think it seems pretty reasonable as a price.