Cost of penny cereal (5)
I believe the answer is:
price
'cost' is the definition.
(price is a kind of cost)
'penny cereal' is the wordplay.
'penny' becomes 'p'.
'cereal' becomes 'rice' (rice is a kind of cereal).
'p'+'rice'='PRICE'
'of' is the link.
(Other definitions for price that I've seen before include "Amount asked" , "Fanny?" , "Betting odds" , "Cost of an item" , "Amount needed to purchase something" .)