Some of the cheapest copies (4)
I believe the answer is:
apes
'copies' is the definition.
('ape' can be a synonym of 'copy')
'some of the cheapest' is the wordplay.
'some of' indicates a hidden word.
'APES' is hidden in the letters of 'cheapest'.
(Other definitions for apes that I've seen before include "Peas (anag)" , "Mimics like primates" , "Copies the primates?" , "Species of primate" , "Parrots" .)