Here is a blade possible for my modular lightsabers. You can adjust the blade size as you want. With the LED lamps I use, there is not much light into the blade. But it's still cool having a blade, and a really cheap one !
I wanted to get a lightsaber, really cheap for cosplays or decoration. I wanted something, easy to make, with no electronic circuit which has to be made each time you construct a saber.
I use a LED keyring torch as a lamp which is at the back of the saber. The light is not very powerful of course, but it could be enough if you are using it in dark places. Moreover, you can add a little piece of plastic to change the color oh the saber (like a Kyber crystal !)
The LED i'm using : Infapower F026 5-LED Keyring Torch
You can find what you need to build the lightsaber here : https://www.thingiverse.com/thing:2751428
I find it perfect for kids who want to get a customisable saber, or as a decoration for your house.