Create a Pop-up Window in Volusion Store

I would need someone that is familiar with Volusion's store to create a pop-up window that will show up at the checkout. In my store settings there is an option to set minimum amount that needs to be met in order to qualify for free shipping on that order. So i would want in that pop-up window depending on the dollar amount that has been set to show customers how much more to add to cart in order to qualify for free shipping. The pop-up window should be similar to the one at this address [login to view URL] , when you add item to the cart it will offer you to buy something else my pop-up should tell the buyer how much more $ to add to receive for free shipping