DIY Project: A Manual Lens From PVC Pipes
Things don't get much cheaper than this. You'll need two PVC pipes of different sizes, a spare camera body cap, a magnifying glass and some super glue. You can already see where we're going with this, can't you? The PVC pipes act as the lens body, the magnifying glass as the optic and the body cap lets you screw it on.
The one thing you'll want to be careful about is getting dust on your sensor. Covering moving parts of your camera with some nylon is a good way to solve the problem, according to the folks over at DIY Photography, who have a full set of pictures and instructions for setting this up.
