Not good value for a bun perhaps (12)
I believe the answer is:
unfavourable
'not good' is the definition.
(unfavourable can mean not good or unfortunate)
'value for a bun perhaps' is the wordplay.
'perhaps' is an anagram indicator.
'value'+'for'+'a'+'bun'='valueforabun'
'valueforabun' anagrammed gives 'UNFAVOURABLE'.
(Other definitions for unfavourable that I've seen before include "Ominous -- critical" , "Adverse" , "Discouraging" .)