Liberate at no cost (4)
I believe the answer is:
free
I believe this clue is a double definition.
'liberate' is the first definition.
(synonyms)
'no cost' is the second definition.
(I've seen this in other clues)
'at' acts as a link.
(Other definitions for free that I've seen before include "Allowed to do as one pleases" , "Not employed" , "Deliver" , "As cheap as can be!" , "Gratis, for nothing" .)