A couple of pounds is everything (3)
I believe the answer is:
all
'everything' is the definition.
(I've seen this before)
'a couple of pounds' is the wordplay.
'couple of' shows that letters should be duplicated.
'pounds' becomes 'l' (L can represent the monetary pound**).
'l' duplicated is 'll'.
'a'+'ll'='ALL'
'is' is the link.
(Other definitions for all that I've seen before include "The whole quantity" , "Fully clad ..." , "'Bless 'em - - ' (song)" , "Every single one" , "The works" .)