This costs only a few dollars, but be sure you get the right item. If you have a good school telescope buy a proper optical solar filter. Mounted correctly in front of a telescope this will give a most impressive picture. Plastic Mylar filters are cheapest, but seem to be extremely fragile and they only transmit a strange, blue colour. These transmit nice colours and beautiful photographs are possible.
Some companies sell solar filters designed to be mounted as an eyepiece.
Avoid these products. One of our students once mounted such an eyepiece solar filter in his telescope. He aimed his instrument directly at the Sun. Solar and lunar eclipses have often been interpreted as bad omens. Several of the proceeding eclipses, and the fear following these , actually changed world history .