A sand rail (also sometimes known as a dune buggy*) is a car stripped down to the barest essentials, as you can see in this video:
The video demonstrates how simple a sand rail really is. A sand rail consists of:
The classic sand rail is powered by the old-style VW air-cooled four-cylinder engine. These engines are cheap, light and easy to work on. They also give reasonable performance in a car that is as light as a sand rail, as seen in this video:
So... Let's imagine that you would like to build a sand rail yourself. First you need a frame. You could design and make one yourself. All that you need is a way to cut, bend and weld steel tubing. But it is easier to imagine buying your frame, and there are many places on the web that are happy to sell you one. Here are a few examples:
Next you need an engine. Again there are a wide variety of suppliers, especially in the VW engine realm. Or you can use a frame that can accommodate bigger water-cooled engines and open up a huge variety of crate engine options. Examples of places that sell VW engines:
And then you need a number of other parts that you can see in this assembly video:
As you can see in the video, it helps if you know how to weld and can do some light machining.
The interesting thing about sand rails is that, once you build one, the skills can help you work on more elaborate projects like this:
Because really, what is an Ariel Atom but an advanced sand rail?
(* Generally speaking, a sand rail has a steel frame and a dune buggy has a fiberglass body like this.)