Died before time at great cost (6)
I believe the answer is:
dearly
'at great cost' is the definition.
('dearly' can be a synonym of 'at great cost')
'died before time' is the wordplay.
'died' becomes 'd'.
'before time' becomes 'early' (I've seen this before).
'd'+'early'='DEARLY'
(Other definitions for dearly that I've seen before include "With affection - at great cost" , "with much suffering" , "Extremely - devotedly - at great cost" , "How I love my wife" , "paying for big mistakes like this!" .)