I have just completed playing through BK the last week finishing today, the song that sticks out the most in my mind is Cheato's Theme when you encounter him ... I have found a half an hour YouTube clip of it, very relaxing
I would put for sure $150 to $250 ($AU). It would be an easy $100 here for a new game anyway from certain retail chains, and the extra would be to help back the project, aswell as extra cool goodies.