If you're looking to go completely remotely robotic, I'd go with a complete setup. You'll save money and time knowing it was at least all working. I'd also recommend you take it to a dealer (or someone who can update the batteries, give it an overhaul). I learned the hard way piecing something together on ebay will likely cost you more in time, money and aggravation. I'm into a Trimble 5603 robot with Nomad data controller for about $5k not including the $900 it cost me to get the internal batteries replaced, calibrated/columated from the local dealer. The 360 deg prisms/ remote units, wires, batteries are not cheap, although I did find cheap battery solutions.
Should you take on the challenge, this forum is a GREAT source for help. Thanks to all those who have helped me.