Not new, but could make half a dollar (3)
I believe the answer is:
old
'not new' is the definition.
('old' is the opposite to 'new')
'could make half a dollar' is the wordplay.
'could make' indicates anagramming the letters.
'half a' means to take half the letters.
'dollar' halved is 'dol'.
'dol' anagrammed gives 'OLD'.
'but' acts as a link.
(Other definitions for old that I've seen before include "Long-established" , "Wild clematis" , "Venerable" , "out of the ark" , "Advanced in years" .)