Treasure sold for a pretty penny (4)
I believe the answer is:
'treasure' is the definition.
'sold for a pretty penny' is the wordplay.
I cannot really see how this works, but
'a' is found in the answer.
'penny' could be 'd' (pre-decimalisation abbreviation for penny) and 'd' is located in the answer.
The remaining letters 'er' is a valid word which might be clued in a way I don't see.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for dear that I've seen before include "Darling" , "Needing plenty of bread" , "Baby" , "Costly (but loved!)" , "close" .)