Hi one thing i´m thinking about
If you need 3 different sizes you could make it like this
Call the pizza with the original prize like "Pizza standard"
Then make a new option with choose field like this
Pizza standard + = 0.00 EUR
Pizza medium + = 3.00 EUR
Pizza big += 5.00 EUR
So if the user choose standard pizza the prize will not change because the price in menü option is set to is 0.00 !
Then you could add an extra menu options for the toppings.
This is just an idea !!
But it would be perfect if the developer of this script could program an extra menü option only for the sizes of a menu for example standard pizza = 3 Euro
Programming an radio button with the first item = checked = 3 Euro
and if the user chooses another price the original price will be changed automatically
thats not a lot of work i would guess