Scandal man's kept under hat, not causing much damage (4,5)
I believe the answer is:
dirt cheap
'not causing much damage' is the definition.
'scandal man's kept under hat' is the wordplay.
'scandal' becomes 'dirt' ('dirt' can be a synonym of 'scandal').
'man' becomes 'che'.
'kept under hat' becomes 'ap' (I can't explain this - if you can you should give a lot more credence to this answer).
'dirt'+'che'+'ap'='DIRT-CHEAP'
(Other definitions for dirt cheap that I've seen before include "attractive to potential buyer?" , "Ridiculously inexpensive" , "Greatly reduced in price" , "doing little damage?" , "next to nothing" .)