Bob,
FWIW, I've priced ballscrews for my X2 mill at $175 that's delivered and with ends machined to suit (I supply the drawing of what I require).
These are for RM1605 ballscrews (16mm diameter) but with your mill, I think RM1204 would be enough and cheaper still.
You can get BF/BK ballscrew supports from the same source or you can make your own bearing housings - there are lots of plans to choose from.
If I wasn't in the process of moving and putting all my tools into storage, I'd be dong the ballscrew/CNC conversion right now.
