Quite a lot.
How Much Does It Cost To Make A Hit Song? : Planet Money : NPR
And they wonder why the music industry is failing to make money. Even just talking about pop music, I've heard many independently written/recorded/released pop songs that are just as good (i.e. catchy, danceable, marketable) as the latest thing being pushed by the major labels. The only thing missing is the advertising/marketing/promotional power the majors have.
Another interesting way to look at this, however, is Nickelback's "How You Remind Me", written by one guy in twenty minutes, recorded by four guys in a studio with a producer, an engineer, and some assistants, barely promoted, and yet took off on its own to out-sell absolutely everything the majors were spending millions on. Since then, the guy behind that song has gone to the other side of the desk, and has written hits for other bands, produced them, and released them on his own sub-label.
[VIDEO]http://www.youtube.com/watch?v=5PRKfj_5Oso]Creating A Hit: 8 Hour Challenge - YouTube[/VIDEO]