Variable prices for toppings dependent on size

[poppypizzeria]

Hey folks. I have a pizzeria and need the following help:

I have 3 pizza sizes: small, large, and extra large.

Extra toppings for a small costs $0.99, $1.99 for a large, and $2.49 for an extra large.

I was able to use this guide to help me make the topping prices contingent on the pizza size. However, it makes all the prices the same if I use the Modifier Group Pricing function.

So, my question is, how can I add an additional two toppings to the topping list that costs more than the rest of these normal toppings? I have two vegan toppings (i.e. vegan mozzarella and vegan pepperoni) that costs $1.99 for the small pizza, $2.99 for a large and $3.99 for extra large. I would like to add these two toppings to the topping list with the exception of their price being higher. 

What's the best way to go about it? Thanks in advance!

[rcmck]

I think the best solution would be to create a another topping modifier group configured the same way just for the vegan/premium toppings.