Excellent outlay including pound I’d added (8)
I believe the answer is:
splendid
'excellent' is the definition.
(I know that excellent can be written as splendid)
'outlay including pound i'd added' is the wordplay.
'outlay' becomes 'spend' (I've seen this in another clue).
'including' is an insertion indicator.
'pound' becomes 'L' (the pound sign is based on an L).
'added' means one lot of letters go next to another.
'spend' going around 'l' is 'splend'.
'splend'+'id'='SPLENDID'
(Other definitions for splendid that I've seen before include "Noble" , "Excellent, magnificent" , "Marvellous" , "'Excellent, glorious (8)'" , "super" .)