Ingredients with custom fields

[AndreaV]

Hello.
A customer wants 4 pizzas. He looks at the product and decide to order pizza marguerita:
a) 1 pizza marguerite (ingredients: tomato, cheese) - $ 2 (base price)
b) 1 pizza marguerite (ingredients: tomato, but no cheese) - $ 2
c) 1 pizza marguerite (ingredients: tomato, cheese, salami more) - $ 2.50 (salami cost $ 0.50)
d) 1 pizza marguerite (ingredients: tomato, no cheese, salami more) - $ 2.00 (salami and cheese cost $ 0.50).

If I insert the ingredients in custom fields with the price I can make case A, case C, case D.
The problem is the case B: if the customer removes the cheese, the pizza costs $ 1.50! I need that, whatever the customer wants to change, the minimum price is the base price.

How can I fix? Thanks

[AndreaV]

I forget: jommla 2.5.17 - virtuemart 2.0.26d