It costs a packet, darling (4)
I believe the answer is:
dear
'darling' is the definition.
(I know that darling can be written as dear)
I don't understand the remainder of the clue.
Can you help me to learn more?
(Other definitions for dear that I've seen before include "love" , "address for partner" , "pet > ducks" , "Treasured" , "close" .)