In principal, anything that makes a sound can be used as a percussion instrument, even your body! It actually gives a great effect if you make percussion out of unusual objects. Some materials lend themselves better than others; you might like to try wood, metal, glass or PVC..
A lot of materials can be found for free, or cheaply at second hand shops.
* Steve Tierra explains how to Make a Shekere on the Djembe-L FAQ
* Advice on Cleaning Cymbals is provided for by Muff
* The Drums and Demonstration Page of the Super Sonic Samba School in San Diego shows an interesting collection of instruments that hardly cost anything.
* A Soup à Gogo is easy to make, costs near to nothing and sounds OK. It can also be used as a Guiro. Great for kids! Take at least two different sized tins, i.e. of soup, beans... Tape them together with two strips of strong tape, with a piece of inner tube of a bicycle (length of the smallest tin adjacent) in between to absorb the vibration. Make sure the bottoms of the tins are aligned. You can tape as many different sized tins together as you like. Hit the bottom of the tins with a spoon; you have an Agogo! The side of your biggest tin is also a Guiro.
* Shakers can be made cheaply and in a variety of shapes and sounds, depending on material and filling. Use i.e. an old storage container, you can find them second hand. When you want to use your shaker at a drumcircle, drum/sambaband, use corn for filling; a very loud and sharp sound.
For playing in a 'melody band', fill your container with tropical bird seed; the fine granules make your shakers sound just like the professional shake eggs.
You could also use a hard wooden (cigar)box to fill the bottom up with seeds. This instrument can be shook in the hand as well as screwed on a stand and be used as a 'shake-woodblock'.
Experiment with different materials and fillings. When you are happy with the sound, glue the top on and... shake it out now baby!
* For Finger Castagnettes, you need two wooden spoons, saw the handles off and drill two holes in every piece, on the side where you've just cut off the handle. Place the two pieces with the hollow sides facing eachother and string them together. Experiment yourself what length of string is comfortable for around your fingers. Besides wooden spoons, you can also use walnut shells.