Seem prepared to whistle for one's money? (5)

I believe the answer is:

purse

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'money?' is the definition.
(a purse contains money)

I cannot understand how the remainder of the clue works.

(Other definitions for purse that I've seen before include "bag for loose change" , "Small pouch for carrying money, mostly by women" , "Contract, crease" , "Winner's prize" , "Pocket" .)

I've seen this clue in the Evening Standard.

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