I notice that a lot of authors, if they use song lyrics in their work (Stephen King is an example here) often have a section where they credit the songwriter and publisher. I’m assuming they had to pay for the use of these, but how much does it cost to use them. What about in other commercial works, or is it a flat fee (I’m aware of the fact that some songs are more expensive than others)? Would you have to pay a royalty for the use of one line from a song in a commercial work, if the song is identified?
IANAL of any kind, and this is a down and dirty explanation of the basic principles of usage rights. My experience with this is almost exclusively within the realms of music publishing and licensing, and some or all of this may not apply to the case in point. There are both legal dopers and copyright savvy dopers who can explain this in much clearer and specific terms.
There’s a statutory rate which applies for the use of copyrighted material, for each instance of use. For example, it might be every copy of a lyric reproduced in a book, the owner of the rights to the lyric would receive X amount of money. I know that it varies considerably based upon the copyrighted work, the medium it’s reproduced or used in, and whether it’s for a performance or simply the use of the work.
In the event of something like a lyric reproduced in a Stephen King novel, the book publisher would contact the music publishing company that administers the rights to that lyric and negotiate a rate schedule. It will be generally be cheaper than paying the statutory rate. However, should permission not be given, generally speaking the copyrighted work can still be used, but the statutory rates must be paid.
If need be i can look up some examples of the agreements and example rates. Again, the exact answers are buried in some of my damn thick entertainment law texts and I’m not going digging in there this time of night. 
I was wondering about this too. In my case I was wondering about songs that include parts of other songs. There have been a couple examples of this recently in popular music, but I can’t remember right off hand what they are. You know what I mean, songs that contain a refrain from an “oldie”.
If an author wishes to use song lyrics, he contacts the songwriter (or the songwriter’s agent). The songwriter grants permission. There is no set fee for this – some songwriters will allow you to use their lyrics for free; others charge exhorbitant amounts (and thus don’t have their lyrics used). It is always the songwriter’s call.
Authors often are expected to have the details in place before their manuscript is accepted for publications, especially if you are writing a short story.
The statatory fee is for the performance of a song, and does not apply to a book. However, if you write a song that includes part of another song, there is a statutory fee.
Thanks for the clarification, RC. The closest I’ve come to the situation we’re talking about here is actually backwards - working with my attorneys to negotiate usage fees for pre-existing lyrics (actually a poem by a well-known author) to be performed on record and published in liner notes. I do remember that it was a lot stickier than just dealing with recording a cover tune.