An expense for the beautiful Ms Wong! (6,5)
I believe the answer is:
pretty penny
'an expense for' is the definition.
I know nothing about this answer so I can't judge whether this works.
'beautiful ms wong' is the wordplay.
I cannot really understand how this works, but
'beautiful' could be 'pretty' (similar in meaning) and 'pretty' is present in the answer.
The remaining letters 'penny' is a valid word which might be clued in a way I don't understand.
This explanation may well be incorrect...
'the' 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" .)