An attractive coin makes a lot of money (1,6,5)
I believe the answer is:
a pretty penny
'a lot of money' is the definition.
(I've seen this before)
'an attractive coin' is the wordplay.
'an' becomes 'a'.
'attractive' becomes 'pretty' (pretty can mean good-looking or attractive).
'coin' becomes 'penny' (penny is a kind of coin).
'a'+'pretty'+'penny'='A PRETTY PENNY'
'makes' is the link.
(Other definitions for a pretty penny that I've seen before include "Large sum of money" , "Fortune" , "Piles of money" , "Millions" , "a lot of money" .)