hey gizeh12 - i work for a music library and occasionally license music to game developers.
Firstly, i agree w/ all of Byron's points - spot on! Second depending on the type of game and the associated budget prices can vary greatly. On a major release console game the top end composers can earn up to $1000 per min of music composed. On the lower end a basic web game may have a music budget of only several hundred dollars all in.