This isn't done yet, and had some extraneous information in it as I was converting a file with much more in it to an interactive web version. This particular file (when complete) will show an interactive breakeven analysis for an event entailing food and beverage.
The link will update as I rebuild the file, but for right now, it's working, and shows that you can interact with the file and have the chart redraw. Probably the best route is to adjust by very large amounts to see the effects. Once I've got it all up and running properly, I'm going to build this into a full page in my site, but I'm uploading for a demo for a client that I need for tomorrow morning.
Here you go, have a play!