I was recently asked to be in a dunk tank at my elementary school's end of the year carnival. As much as I love being continuously dropped into a tank of cold water by vindictive elementary students, I instead offered to make a game.
What I came up with is a jumbo sized version of the game Operation. It looks, acts, and works exactly like the fun board game of old. Best of all it wasn't very tough to make and cost under $10. Had I planned this far in advance I could have had some of my students help do the work, since most of it involves painting and cutting.
Time: 3-5 hours
Cost: Under $10
A Flat Panel TV box. Or any other wide and flat box.
Metal Tongs ($1)
Tin Disposable Oven Trays ($1 for 3)
Buzzer ($3) - I used two of them because I had two. Or just get one big one.
AA Battery Holder ($1.50)
Red LEDs ($1-5) - Use 10mm Diffused Red LEDs if you can.
Resistors (100 for $1) - Might not be necessary depending on how you do the power.
Wire - You need stranded wire for part of this project, make sure you have some on hand. Solid core will not work (it will eventually break.)
Tape (packing, electrical, and mounting tape)
To be honest you probably have most of this stuff around your home right now. I only needed to go out and buy the tongs and tin oven trays. My total cost for this project was under $5 and would have been less but I bought extra supplies.
The one thing you have to watch out about is making sure your tongs and tins are conductive. This is why I listed a Multimeter as a tool you should have. If they're not conductive then your game isn't going to work.
Now you could always make this solar powered... which would be fun filled and completely pointless. If so you can always get supplies from my website, Brown Dog Gadgets. I also have battery holders and LEDs if you're in need.