I plan on building my own by using a 400w servo and a planetary gearbox like this:
NEW IN BOX HARMONIC DRIVE SYSTEMS HPG-20A-21-J6GCK PLANETARY GEAR REDUCER | eBay
I have two of these gearboxes with zero backlash.
Just need to get an adapter made to mount a wood lathe chuck.
I bought a used wood lathe tailstock on Ebay to use.
Total cost will probably be about $1000.
Gearbox - $250
Servo and drive - $450
Tailstock - $50
Chuck - $100-$150