Associating Properties With Array List Elements?

In my project I need to create a pizza ordering system. I have created a array list of pizza toppings and each pizza topping must have a cost property associated with it, then the user can pick the toppings they want and the cost of each topping will be added up and the total cost of the whole pizza will be displayed. But I don't know how to associate a cost with each topping. I have been told that I can access the cost through a get/set method and store it in a private member variable. But I don't know how to do this?

I've tried to do it, but it hasn't worked. This is the code

public void setCost( double cost){ //my get/set method
this.cost = cost;
}
public double getCost(){
double price = 0;
return price;

[Code] .....

But there is an error on each of the ingrediantCost method lines, saying

The primitive type double of cost does not have a field Pepperoni

...and the same for chicken, ham and onion.