// get the index for the PGS and PRpO and if they are selected then deduct $2
var pepperoni = toppingsCheckBoxList.Items.FindByText("Pepperoni (+$1.50)");
var greenPepper = toppingsCheckBoxList.Items.FindByText("Green Peppers (+$0.50)");
var sausage = toppingsCheckBoxList.Items.FindByText("Sausage (+$1.00)");
var redPepper = toppingsCheckBoxList.Items.FindByText("Red Peppers(+$0.75)");
var onion = toppingsCheckBoxList.Items.FindByText("Onion (+$0.75)");

try
{
if ((pepperoni.Selected &&
greenPepper.Selected &&
sausage.Selected) ||
(pepperoni.Selected &&
redPepper.Selected &&
onion.Selected))
totalCost -= 2.00;

// return the total
totalPrice = string.Format("Total: {0:C2}", totalCost);
}
catch(NullReferenceException nre)
{
totalPrice = string.Format("Error: {0}<br/>{1}", nre.Message, nre.InnerException);
}