Is your friend having a bad day? Send them that favourite part of their favourite song and put a smile on their face.
Using songs from your iTunes Library, select a small section of a song that has certain lyrics that you know your friend will love, crop it, and send it to your friend. When your friend opens the message, the song clip will play. After it plays once or twice, it can't be opened again. Once it's closed, the clip title will appear as a blue link. When the link is clicked, your friend will be directly sent to that specific song in the iTunes Store, which will make it easy for your friend to by it, if they don't own it already If they do own it, they won't need to click on the link.
This is a rough idea of what I'm thinking about. I have some more apps that I'm thinking about, but I want to start off with one.
As for price, I'm not sure what to look for.