I'm in the process of organising a charity murder mystery night.
When I first looked into it, it seemed really expensive and hardly worth it, until I found a local am-dram group who do them.
Going by my preliminary calculations, I expect to make around �1,000 on the night, after overheads. But if you were really brave, you could just buy the box on how to do your own, and customise it. small prize for the table who solves it!
Of course, it depends where you're based on how much it would cost to set up in the first place!
It was also recommended by one of the murder mystery companies that I had a silent auction on the same night, by asking local companies and shops to donate items for auction. But I think that would be a bit ambitious for my first attempt!
Another thing that I often see around here is car washes. If the groups you are in are large, then you could rope everyone in to help.
Or bag packing at your local supermarket, especially around Christmas. You'd probably get more volunteers to help with this too.