Costlier (6)
I believe the answer is:
dearer
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">costlier</span>' is the definition.<br/ ><span class="explanation-format__explanation">('dear' can be a synonym of 'costly')</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for dearer that I've seen before include "Nearer to the heart" , "More expensive or loved" , "Less cheap" , "More expensive or more beloved" .)