Consoling words are twice as costly (4,4)
I believe the answer is:
dear dear
'consoling words' is the definition.
'twice as costly' is the wordplay.
'twice' shows that letters should be duplicated.
'as costly' becomes 'dear' (synonyms. I am not sure about the 'as' bit.).
'dear' doubled is 'DEAR DEAR'.
'are' acts as a link.
Can you help me to learn more?
(Other definitions for dear dear that I've seen before include "Expression of dismay" , "That's a pity!" , "Too bad!" .)