DIY Jacob's Ladder
The Jacob's Ladder is one of the most iconic scientific special effects of all time. Using a few common things laying around the house, and with some bargains you should be able to complete this project from under $100.
These were popular in many science fiction movies from the 1920s through the 1950s. The simple Jacob's Ladder creates an electric arc which climbs a pair of electrodes mounted at an angle. All you should need to build one is a 12 x 18 inch wood board that's ~1 inch thick, two copper or brass rods 1/8 inch in diameter(coat hangers work great for this), a high voltage neon power supply, a few screws and electrical tape. Mount the power supply on the board with screws. cut the two leads 5 inches long and strip off the last inch of insulation from each lead. Bend a small loop in the end of each rod, shape the lower inch extending from the loop into a gentle arc and use screws to attach the rods to the board. You want the screws about 1 and 1/4 inches apart. By rotating the rods around the screws the distance between the curved lower sections of the rods can be adjusted. Wind the power supply wires around the bottoms of the electrodes and insulate them with electrical tape. Adjust the spacing so the bottoms of the electrodes are 3/4 inch apart. Being careful to keep the rest of the robs straight, bend them so their tops are 2 and 1/4 inches apart. Your's will probably require some adjustment after puttin it all together to get a consistent arc. You now have a working Jabob's ladder.
In a correctly set up ladder the arc will travel all the way to the top where the wires have a sharp outward bend in them to pull the arc apart to the point that it extinguishes and the whole process starts again at the bottom. If you are having difficulty getting the arc to strike at the bottom it may be nessicary to add a Gabriel electrode between the base of the two main electrodes using a 2 Megohm resistor and a spare piece of wire.