Cost of cigarettes? (6)

I believe the answer is:

packet

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'cost of cigarettes?' is the definition.
Although both the answer and definition are singular nouns, I cannot understand how they can define each other.

This is the entire clue.

Can you help me to learn more?

(Other definitions for packet that I've seen before include "Container - ship" , "Small fortune - carton" , "Mail ship" , "A boat; large sum of money" , "Small parcel" .)

I've seen this clue in the Evening Standard.

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