How hard would it be to make a rail like this?

As seen in the behind the scenes video … the blue rail …

Here is the actual production video …

The basic mechanics are not that hard.
Controlling/ damping/ isolating vibrations that will affect the camera are.
Which is why the good stuff is $$$$$.

We actually had some MakerSlide for this very purpose. Who knows where the extrusion and carriage is now? It was in the media room back in the day.