Liberate at no cost (4)
I believe the answer is:
free
I believe this is a double definition.
'liberate' is the first definition.
(I know that liberate can be written as free)
'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" .)