One of the coolest things about coil guns is that they're powered by electricity. Usually, if you want to DIY one, the coil itself is the most expensive part. Don't want to buy one? You can either make one yourself, or steal one from another device you aren't using like How To Lou did with his electric stapler turned coil gun.
To build it, Lou used the coil from an electric stapler, some PVC, and a few other small things you probably have lying around like electrical tape and a nail. Once he removed the coil, he made a barrel from PVC to attach to the stapler. He used kept the stapler's trigger mechanism and sawed off a piece of metal from a long bolt to use as the projectile.
It may not shoot 20,000 volts like the Tesla gun we saw a few months ago, but it's probably one of the simplest coil guns you could ever make. Check out the video for step-by-step instructions and visit Lou's website to see more of his projects.