Apple's Garage Band app for iPhone and iPad is free today. (Oct 27, 2013) It does list a complete set of instruments as a $4.99 in-app purchase. It is also 610 MB. Don't know how long the free lasts.
It looks like Garage Band is free for devices running iOS 7 and the other Apple apps are free for devices activated (purchased) on September 1, 2013 or after.
Apple is charging for the other apps on devices purchased before September 1, 2013 - correct?