You can add a pull down menu for surcharges, but this is only available within ShopSite Pro. You would go to Commerce Setup > Order System > Shopping Cart, and scroll down to the surcharges field. You would set up the surcharge pull down the same way that you set up ordering options for a product. More information about setting up the surcharge can be found at the following URL:
http://www.shopsite.com/help/8.3/en-US/ ... harge.html
-Lauren