TOPIC: show a running total on registration page

I'd like to see a box that changes as people start clicking items that have a $$ value. So, when they click on a certain checkbox that has a value of $50, the box shows $50. Then if they click on another box that is for $25, the box changes to $75. This is pretty typical of some registration extensions I've seen for another CMS.

I would love this as well.