Lettuce and tomato's opening price (4)
I believe the answer is:
cost
'price' is the definition.
(I know that price can be written as cost)
'lettuce and tomato's opening' is the wordplay.
'lettuce' becomes 'cos' (cos is a kind of lettuce).
'and' is a charade indicator (letters next to each other).
'opening' indicates taking the first letters.
The first letter of 'tomatos' is 't'.
'cos'+'t'='COST'
(Other definitions for cost that I've seen before include "Come to" , "Charge" , "Amount to pay" , "Suffering" , "Outlay required to buy" .)