@Sara007 - Making a solar cell is a lot of fun but don't expect it to give off much energy. While your sun jar lamps are powered by a professional grade solar cell, the ones you can make at home out of copper and house scraps are move for demonstration rather than anything else.
There are some auction sites that sell sheets of solar cells at reduced prices, so in theory you could make your own solar panels cheaper than you could purchase them. I guess it all depends on what you want to do with the solar cells once you have them. No matter what, have fun with the project. It's great to hear that kids are interested in science.