Attractive girl is worth a lot (6,5)
I believe the answer is:
pretty penny
'worth a lot' is the definition.
I don't know anything about this answer so I can't judge whether this works.
'attractive girl' is the wordplay.
'attractive' becomes 'pretty' (pretty can mean good-looking or attractive).
'girl' becomes 'penny' (woman's name).
'pretty'+'penny'='PRETTY PENNY'
'is' is the link.
Can you help me to learn more?
(Other definitions for pretty penny that I've seen before include "Large amount (of cost)" , "A tidy sum of money" , "Large sum of money" .)