Tubescope: $0-20 Refractor Telescope with camera mount

Now you too can be Galileo! Inspired by Cosmos and the recent eclipse, this refractive telescope gives you a Galileo experience out of things you may already have around the house, or at worst $20. There are two versions - a fairly impressively decent handheld telescope you can look through, and a camera lens version which works like a powerful (though fuzzy - depending on quality of the lenses) telephoto lens. The lenses used are 40.5mm filter-style close-up lenses - the type that screw on to the end of a camera. Cheap lenses give a beautiful low-fi look with purple chromatic aberration.

To build, you'll need a 60mm inner diameter cardboard tube, like the Tu2 Mailing Tube from Australia Post. This tube needs to be cut down to about 60cm long for the handheld and about 50cm for the camera version. You'll also need a 40.5mm +2 Close-Up filter, which you can get on ebay pretty cheaply, and for the handheld version you'll also need a +10 Close-Up filter. A kit of four filters including those two go for about $17 on ebay.

Future ideas: fully 3d printed body, improved focusing, kit version with everything shipped inside the tube, cheap reflector telescope, rotating mounts, mounts for different cameras