Expensive fur bishop entered in auction (5)
I believe the answer is:
sable
'expensive fur' is the definition.
(I've seen this before)
'bishop entered in auction' is the wordplay.
'bishop' becomes 'B' (chess abbreviation).
'entered in' indicates putting letters inside.
'auction' becomes 'sale' (I've seen this in other clues).
'b' going inside 'sale' is 'SABLE'.
(Other definitions for sable that I've seen before include "fur coat" , "Marten's fur - dark black" , "Type of fur" , "Dark brown fur of the marten" , "Black (heraldry); fur" .)