Maybe a stupid question: but do you need iTunes to install an .ipa file? I've seen some programs that can just install these files on any iDevice without the use of iTunes.
And isn't Xcode and an Apple acount enough to sign the app?
Are you talking about distributing ipa files outside of the App Store? As I understand it, you also need $100/year and you're limited to provisioning 100 UDIDs. I don't think this is actually an alternative.
The app maker could sell a XCode project. Each end-user would pay Apple's $99 license fee, provision their own devices, and sign the app with their own key.
And isn't Xcode and an Apple acount enough to sign the app?