Normal bargain for root vegetable (7)
I believe the answer is:
parsnip
'for root vegetable' is the definition.
(parsnip is a kind of root vegetable)
'normal bargain' is the wordplay.
'normal' becomes 'par' (I've seen this in another clue).
'bargain' becomes 'snip' (slang term for a good deal).
'par'+'snip'='PARSNIP'
(Other definitions for parsnip that I've seen before include "Yellow root vegetable" , "Plant with edible white root" , "Type of root veg" , "Pale carrot-like vegetable" , "Spar pin (anag) - vegetable" .)