Small game, huge size?

The size limit is 100 MB with iOS 7, not 50 MB anymore.
http://www.macrumors.com/2013/09/18/apple-increases-over-the-air-app-store-download-limit-to-100mb/

But I would check your final app export, sounds like something is wonky. Do you have any post processing scripts or any plugins that copy extra files to your iOS build after the Unity compilation is done? For instance, even though you are only exporting < 1 MB of sound files, if you want to play notifications, those sounds have to be exported as part of the app bundle, so maybe you are copying some really large notification sounds into the iOS project after the Unity project finishes building. Or maybe some plugin you downloaded into your project has some very large database that it copies over (that would be bad). Once your iOS app builds, you can go into the app bundle itself to find the culprit. (sorry it escapes me, but google has details, basically open a terminal, cd into the .app file, then do some ls commands to find the largest files in the bundle.).

Also, if you are just Append'ing to the iOS build, maybe try creating a fresh export from Unity (i.e. export to new directory).

Lastly, you can view which files are in your build in XCode, so maybe take a quick look in XCode's file hierarchy for anything weird before doing all this other stuff.