I'm currently *entertaining* the idea of creating a native iPhone app that interacts with my XenForo installation in a unique way. I'll be sure to post here on the forums about it if it actually goes live. The app itself will function for more then just reading the forums, it will also interact with a specilly crafted database and such, but maybe I'll release the classes I write for the message board portion only.
I really disagree with the above pricing - if I were to do something similar I would charge $99 for the app project files, and a minor fee for major upgrades (if any major upgrades were to ever occur). That's what I find fair - especially if you want the App released under your company's name and have to pay another $99 fee for releasing it to the store.