Use data from gravity form field and insert it into a popup on the same page

Hi everyone. I am using Gravity Forms to collect data for a form. I’d like to use the sum-total of the form to be used in a modal popup on the same page. ie - when calculate my rate button is pressed a modal popup is activated with the sum-total figure in it. I am not sending the data to another url or another gravity form. I am stumped and have no idea how to do it. thanks