Extra purchase picked up (3)
I believe the answer is:
bye
'extra' is the definition.
(bye is a type of extra in cricket)
'purchase picked up' is the wordplay.
'purchase' becomes 'buy' (buy is a kind of purchase).
'picked up' indicates a 'sounds like' (homophone) clue.
'buy' is a homophone of 'BYE'.
(Other definitions for bye that I've seen before include "So long" , "Run not off bat" , "Extra run in cricket" , "See you" , "Stay out of round" .)