The cost in pence for a cereal
I believe the answer is:
price
'the cost' is the definition.
(the cost or price of something)
'pence for a cereal' is the wordplay.
'pence' becomes 'p'.
'for' says to put letters next to each other.
'a cereal' becomes 'rice' (rice is a kind of cereal).
'p'+'rice'='PRICE'
'in' is the link.
(Other definitions for price that I've seen before include "What has to be paid" , "Cost of purchase" , "Fanny?" , "Fee" , "Amount needed to purchase something" .)