Game is extremely pricey (1-3)
I believe the answer is:
i-spy
'game' is the definition.
'is extremely pricey' is the subsidiary indication.
'extremely' says to hollow out the word (remove centre letters).
'pricey' becomes 'pricy' ('pricy' can be a synonym of 'pricey').
'pricy' with its middle taken out is 'py'.
'is'+'py'='ispy'
(Other definitions for i-spy that I've seen before include "Children's alphabet game" , "Children's observational game" , "Children's guessing game" , "Wordgame" , "Child's guessing game" .)