You can add a shopping cart like PayPal or 2Checkout to your website. Those seem to be the most popular shopping carts on the Internet.
This is done by copying and pasting html button code into the HTML tab in Ewisoft Website Builder. You may also be able to add a shopping cart through your web hosting provider control panel on the Admin side.
The cost would be whatever your shopping cart provider charges. This can be a transaction fee or a transaction fee based upon a percentage.