This game is really good, and it's only a $1.99 on the android store and the free version isn't that limiting.
Every 100,000 people that download the paid app version will unlock 10 songs, and it will go up to 100 free songs included in the app overtime (aka a million downloads)
It has really cool music in the game, electronic music mostly but some are classical violin combined with techno and other cool things.
it's worth it.
here's gameplay footage: