Bar with a great deal: they don't cost much (7)
I believe the answer is:
buttons
'they don't cost much' is the definition.
(something worth a button is not worth much)
'bar with a great deal' is the wordplay.
'bar' becomes 'but' (both can mean 'except for').
'with' means one lot of letters go next to another.
'a great deal' becomes 'tons' (both can mean a large amount).
'but'+'tons'='BUTTONS'
(Other definitions for buttons that I've seen before include "Fastens" , "Secures" , "may be at work in hotel" , "They secure" , "Fasteners for the Cinderella character" .)