I put together a spreadsheet a while back to play around with calculating profits. It can be a real eye-opener as to how you are really doing or what you need to be doing as far as number of events and what you are charging. It gave me a way to see how charging less was affecting the business.
It's just a basic spreadsheet, still need to take into account all the little things that add up too, but I put several of the big ones in there though. Feel free to change it as you need to. All of the Orange fields are the ones you can edit (spreadsheet is not locked), such as tax percentages, and your overhead may vary so those
can be updated. The rest are formula fields and shouldn't be changed unless you know what you're doing.
I've shared it on Google Docs here: https://docs.google.com/open?id=0B-9x7WDs5L8GM2ZleDlkVV95ODg
You'll need click File>>Download or if you've got a Google account you may be able to Export it to a copy as a Google Spreadsheet (File>>Export to Google Spreadsheet) and work in it directly from Google docs.