Adding a calculation to add extra cost to total
My product is $200 but a larger size is $50 more. I edited the TotalPrice calculation like this [price]+[option]*[quantity] and this works perfectly up to a point. If a customer wants to buy a second one of the same item it only adds the extra $50 not the cost of the item ($200).
I am giving the option as <input type="radio" name="eCart1_1_FourInchOption_Add" value="50" />.
Any advice would be greatly appreciated.