Product options - for pizza topping selection

hi,
Using opencart_v1.5.1.1 for pizza ordering.

i want to set the product options for topping selection.
eg: 1 LARGE PIZZA, 3 TOPPINGS costs $10.00 (this includes 3 toppings which a customer can select).
but when a customer wants to add additional toppings, the price of that selected toppings shall be added to the pizza price

$10.00(3 toppings included) + $1.00 (extra topping 1) + $1.00 (extra topping 2) = $12.00

i can't assign price to all toppings options as customer has to select 3 toppings which comes free with pizza.

1) To start with,i used the location field in the backend as topping limit.
2) Then with following link, i limited the topping selections(i used the checkbox only for toppings selection and passed the option value dynamically instead of manual addition)
http://hotwebideas.hubpages.com/hub/jqu ... -of-clicks

Now it pops out message if customer exceeds the topping selection limit.

Is there a way so that if a customer exceeds the topping limit, the price of additional toppings starts adding to the pizza price?

thanks...

anyone having a suggestion

thanks...

any solutions?

thanks...