Advantageous purchase provides pub with profit (7)
I believe the answer is:
bargain
'advantageous purchase' is the definition.
(I've seen this before)
'pub with profit' is the wordplay.
'pub' becomes 'bar' (both are drinking establishments).
'with' means one lot of letters go next to another.
'profit' becomes 'gain' (synonyms).
'bar'+'gain'='BARGAIN'
'provides' acts as a link.
(Other definitions for bargain that I've seen before include "Special offer" , "Cheap acquisition" , "Thing bought cheaply" , "special deal" , "Deal; cheap buy" .)