The Muse DLC will cost you $11.99. Alternatively, the tracks can be purchased separately for $2.99 each. Those on the PS3 are currently not able to purchase the DLC as a pack -- for some reason it won't be hitting the PlayStation Store until January 7, though you can still purchase the songs individually.
Here's a half hour of the Arkham Origins Mr. Freeze DLC, if you want to watch that
11:45 AM on 04.15.2014