Liberate group at no cost (3,4)
I believe the answer is:
set free
'liberate' is the definition.
(synonyms)
'group at no cost' is the wordplay.
'group' becomes 'set' (both can mean a collection).
'at no cost' becomes 'free' (I've seen this before).
'set'+'free'='SET FREE'
(Other definitions for set free that I've seen before include "without the box" , "Release, remove restraints" , "Uncaged birds have been" , "Turn loose" , "no longer confined" .)