Necessarily gets a little cheaper, for certain (8)
I believe the answer is:
perforce
'necessarily' is the definition.
(I've seen this before)
'a little cheaper for certain' is the wordplay.
'a little' indicates the answer is hidden within the clue (a little bit of the clue).
'PERFORCE' is hidden in the letters of 'cheaper for certain'.
'gets' is the link.
(Other definitions for perforce that I've seen before include "willy-nilly" , "Of necessity" , "Old word for necessarily, due to circumstances" , "By force of circumstance, necessarily" , "Unavoidably" .)