@krammet
I looked at your stores settings and i did the first thing that ANYONE should normally do to debug.
Disable all plugins besides WP e-Commerce and Gold Cart if available.
Just doing that and your calculator is working again.
This looks like you are having a conflict with another plugin. You will have to disable all plugins and enable them one by one while checking after each plugin activation to see if the calculator still works.
Also you might want to try changing to the default 2010 theme from wordpress and see if it works in that. If it does then its something with your theme.
I looked on the themes vendor
s page and i don`t see any references of it being compatible with the latest WP e-Commerce version and not even a mention of WordPress 3.9 compatibility so you might want to talk to the theme creator too.
I`ve seen a few javascript issues too cause by the theme.
https://dl.dropboxusercontent.com/u/16683640/Screenshots/2014-05-05_2341.png
This is valid for everyone else out there that is having issues.
First thing disable all plugins and change to a WordPress theme (2010 preffered).
If it works in that then its your theme or a plugin conflict thats causing the issues.
Regards
Mihai