Here's a simple design for a vacuum chamber that can be built for between $10 and $20, depending on how much one can pull from the garbage.
The wooden frame is cut down from an old bookshelf that someone was throwing out. The glass dome is an upside down flower vase I bought from a charity shop.
The heart of the machine is a vacuum pump. I pulled this one from a refrigerator that someone else was throwing out. There are two copper pipes that come out of the pump, one is suction (which we use), the other is pressure (which we ignore). The original wiring harness is routed through a light switch, and then to the refrigerator's power cord.
There are four components that have to come together without any leaks: the vacuum pump, the vacuum chamber, the pressure gauge, and the relief valve. To do this I bought something called a 1/4" NPT Thread 4 Ways Cross Connector Pipe Adapter Coupler.
A pressure gauge that measures from normal atmospheric pressure down to zero is invaluable for determining the quality of the vacuum and debugging any leaks in the system. A relief valve allows one to dump the vacuum in a controlled manner.
The hardest component to get right was the seal. I used silicone frisbee intended as a dog's toy for the base. But that's not enough, since the glass rim on the vase is not perfectly level. So I used a toaster oven to liquify two sticks worth of hot-melt glue to the underside of the frisbee. Then I dropped a circular disk of 3mm plywood onto the frisbee, flipped it over, and while the glue was still hot, pressed the vase down onto the frisbee. The exact orientation of the vase at that moment needs to be permanently recorded with reference marks, since no other orientation will seal.
Another feature of the seal is a pair of copper wires that go through the wood and the frisbee. They are designed to be alligator clipped to from both inside the vacuum chamber and outside, so that power or data can be obtained in the vacuum. For example, one might want to demonstrate that the sound from an electric buzzer disappears as a vacuum is pulled.
Here's a video of the vacuum chamber being used to determine why pears sink while apples float.