A Monorail motor costs 50$, so I decided to design a Monorail motor.
This motor uses one ball bearing with the diameter of 9mm, 3mm high and a hole of 5mm. You also need 2 metal axles with the measurements 25mm x 2mm.
These parts were printed on a prusa mini with 0.1mm layer height and Maertz PMMA-1002-005 Polyactic-Acid matt PLA Filament, you might need to adjust tolerances on other setups.
See a video of it running:
The author marked this model as their own original creation.