Thanks for the feedback. I've been hesitant to add anything more than just list items because they would add complexity both for the user and in my code. However, adding descriptions or some other organizational element seems like it could be useful. If I remember correctly, 37s allows you to add organizational headers or breaks in backpack.

As for pricing, I'm not sure what I'm going to do yet. For now I'm considering just putting up a couple ads, though honestly I hate ads. The other option I'm considering is some kind of freemium model. If I go the freemium route, I'll probably give stripe a try.