Lawyers profit with a cheap buy (7)
I believe the answer is:
bargain
'a cheap buy' is the definition.
(I've seen this before)
'lawyers profit' is the wordplay.
'lawyers' becomes 'bar' (I've seen this before).
'profit' becomes 'gain' (synonyms).
'bar'+'gain'='BARGAIN'
'with' acts as a link.
(Other definitions for bargain that I've seen before include "Advantageous purchase" , "understanding" , "Count on" , "Agreement; cheap item" , "Cheap offer" .)