Costing nothing (4)
I believe the answer is:
free
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">costing nothing</span>' is the definition.<br/ ><span class="explanation-format__explanation">(given away for free)</span><br/ ><br/ >This is the entire clue.<br/ ></span>
(Other definitions for free that I've seen before include "Untie" , "Under no obligation" , "Gratis, for nothing" , "Not busy" , "Not confined" .)