Amount to pay (5)
'amount to pay' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for cost that I've seen before include "Come to" , "Amount required as payment" , "Be priced at" , "Charge" , "Amount to pay" .)
(Other definitions for price that I've seen before include "Jordan?" , "Amount needed to purchase something" , "Fee" , "Betting odds" , "Amount asked" .)