The first version worked, but wasn't easy to daily drive due to the lack of bearings, static or otherwise.

I grabbed some cheap 3mm ceramic bearings, and after a great deal of trial and error, rigged up a working case. 

The smoothness is now good enough to use for my programming job.

I also played around with different options for the trackball itself. The original phenolic resin ball has a medium weight and good smoothness. A steel bearing is heavier and a bit more satisfying, but isn't always as precise due to its reflectiveness. I've settled on an POM ball. Cheap, light, and precise. Almost too light, but for me at least I've found it to be the best option.

The cost is still too high. If sourcing the components from Alibaba, it still comes to around $12 for the whole assembly.