Do you know how rare it is to have a "canned" shopping cart with the ability to fairly easily do complex pricing options on a single item? Maybe you do, but if you don't... basically, they don't exist! I have looked. Everywhere! And the few that might even come close to the functionality that you have in CornerStore cost a fortune!
The work, the thought and the organization you put into this app is incredible.
I looked all over trying to find a simple cgi script. I found that FileChucker was by far the best. If you have issues with your hosting service's php.ini max upload size then this is the way to go. Looking forward to future enhancements.