Value a bit of profit on grain (5)
I believe the answer is:
price
'value' is the definition.
(price is a kind of value)
'a bit of profit on grain' is the wordplay.
'a bit of' says to take the initial letters.
'on' is a charade indicator (letters next to each other).
'grain' becomes 'rice' (rice is a kind of grain**).
The first letter of 'profit' is 'p'.
'p'+'rice'='PRICE'
(Other definitions for price that I've seen before include "Fanny?" , "Cost of an item" , "Value - figure" , "Amount for which a thing is sold" , "Cost of purchase" .)