Electrophoresis
Electrophoresis boxes are easy to make but pretty expensive to buy. They are nothing but electrodes in a box. I also created a separated box for pouring the gel with a comb to make the wells in a gel.
For proper measurements I just roughly copied the size of commercial units.
Diagram: schematics of an electrophoresis box.
Image: design in Fusion360 ready to be printed out.
Image: printed result.