The "base price" is the price for the product without any options chosen. For example, the All-in-one Service Folio has a base price of a certain amount. That is for the imitation leather (leatherette) product with the Bible pouch designed for the Bible. In the “Select Color” drop-down list if you choose your color in imitation leather there is no price change. However, if you choose to upgrade to leather in one of the colors for an increase in price as shown in the drop-down menu.
The same goes for Bible and book covers and most other products. The base price is the price for the product in imitation leather. Upgrading to leather will increase the price accordingly. This price increase is shown clearly in the drop-down menu where you select the option.
It's a good idea to always click the black "update" button before adding it to your cart (see illustration to the right). That way, you will get the final updated price, including the options you have chosen.