The PowerUp Electric Powered Paper Airplane Conversion Kit from TailorToys will turn a homemade folded paper airplane into an electric powered propeller driven plane. It comes with one propeller module and a charger module which runs on 3 AA batteries. You will need to supply your own paper to fold your plane. Once folded, clip the propeller module in place and charge it. 20 seconds of charge time will fly your plane for around 30 seconds or so. This looks like it could be a lot of fun for less than $20. You can get yours at Amazon.com
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Or you can buy really nice rubber band powered airplanes for $7.00 complete with brilliant paint job and landing gear. Flies 100 feet and no batteries required.