King's son in north cutting cost (6)
I believe the answer is:
prince
'king's son' is the definition.
(I've seen this in another clue)
'north cutting cost' is the wordplay.
'north' becomes 'N' (abbreviation).
'cutting' means one lot of letters goes inside another (some letters cut their way into a word).
'cost' becomes 'price' (the cost or price of something).
'n' going within 'price' is 'PRINCE'.
'in' acts as a link.
(Other definitions for prince that I've seen before include "Monarch's son" , "Son of a sovereign" , "Canadian province" , "Machiavellian ruler" , "Royal personage" .)