Less expensive (7)
I believe the answer is:
cheaper
'less expensive' is the definition.
('cheap' can be the opposite of 'expensive' so perhaps 'cheaper' is reasonable for 'less expensive')
This is the entire clue.
(Other definitions for cheaper that I've seen before include "Comparatively despicable" , "more affordable" , "Less costly" , "More reasonable" , "Less expensive or tasteful" .)