Vegetable is equal bargain (7)
I believe the answer is:
parsnip
'vegetable' is the definition.
(parsnip is a type of vegetable)
'equal bargain' is the wordplay.
'equal' becomes 'par'.
'bargain' becomes 'snip' (slang term for a good deal).
'par'+'snip'='PARSNIP'
'is' is the link.
(Other definitions for parsnip that I've seen before include "A white root vegetable" , "Pale carrot-like vegetable" , "Sweet root vegetable" , "Spar pin (anag) - vegetable" , "Tapering vegetable" .)