How much should you expect to pay for royalty free music
Quick Answer:
From what we have seen on most of the royalty free music sites you should expect to pay

$24.95 to $49.95 for a full length track of 2 minutes or longer.
and $9.95 and up for a short music loop.

The Reality
There still seems to be a very wide range of prices and licensing options across the board for royalty free music. There are two basic kinds of pricing structures at the moment,

1. Pay a one-time fee no matter what the use of the music will be.

2. Pay a fee based on how you are going to use the music, how many copies will be made, distribution, budget of the project, etc.

Here are some examples:

The first option is usually the least expensive especially if the royalty free music provider does not ask you to submit cue sheets for each performance of the music. Companies like Partners In Rhyme and Musicloops.com a very affordable in this regard.

The second option can be very expensive, both in up front cost and royalties paid for each performance of the piece. The royalty free websites using these pricing structures and licensing fees are not actually selling royalty free music but more of the old fashioned needle drop or production music library pricing structure.