I've been playing the guitar for over 8 years and the piano for now about 4 years. I can make a song for any special occasion : birthdays, love declarations, or even for your WoW guild. Whatever you want !
The price will depend on the quality of what you are looking for : whether it's a simple 30 seconds singing + guitar composition about the subject you choose (5$), a cover of an actual song (10$) or a complete work with several instruments in the ambiance you like (20$ per minute).
You can see my skills here and judge accordingly :