For my standards, my bucket polisher works great.
I'd hand polish before I spent $500.
One highly significant (and unique) superiority of the Diamond ball cleaning/polishing machine that we use, is its patented "spiraling" capability. While the balls are obviously rotating around a nominally horizontal plane, the effect of this additional spiraling feature is that every square millimeter of the ball's exterior surface is contacted by the cleaning elements many times throughout the cycle.
Think of it as the 100% coverage of points anywhere on the Earth's surface by a hypothetical satellite rotating on infinitely variable orbital planes.
I really like the design of the diamond polisher. I think I'll rip it off when I build another one. Can probably do it for $150 if I keep my eyes open for a good 2nd hand motor.
Here's a design that improves on the 16-ball Diamond machine...
It has an offset platter that imparts 'spin & tumble' to the balls. Works really good but a real pain to build with just basic woodworking equipment. A large CNC machine would be nice. Strictly parts/materials is a bit under $200, labor is free if you like building stuff with close tolerances.
Yes, I've launched some balls out of some experimental versions, that's why I don't like the revolving platter idea too much (whipping 6 lbs of hard balls around in a circle).
That's a nice design. Is it your design? I wonder if an industrial sewing machine ebay special motor would work fine for it. You might be able to reduce the height if its shorter than the motor you used.
I was thinking a cheap drill press would have all the basic parts you'd need, with very little needing modification.