Enter an Amazon Wishlist ID here and the total cost of all the items will be displayed below. If you leave the box blank and are signed into Amazon, your default wishlist will be used.
You will need to turn off web security for this to work. Such is the caveat for having it run in your browser. This is because it needs to connect to the Amazon website and so forth. You can see all the code in view-source, and you can see it's not doing anything bad.