Price finally cut for a leafy vegetable (3)

I believe the answer is:

cos

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'for a leafy vegetable' is the definition.
(cos is a kind of leafy vegetable)

I can't explain the remainder of the clue.

Can you help me to learn more?

(Other definitions for cos that I've seen before include "Islanders here" , "vegetable?" , "A long-leaved lettuce" , "Island in Mediterranean" , "Kind of lettuce in microcosm" .)

I've seen this clue in The Independent.

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