How to convert manual Lathe into CNC Lathe?
I would suggest reading this article,
"Beginner’s Guide to CNC Conversions," at
http://www.dakeng.com/CNCconvert.html
This will cover the basic elements that need to be included in a conversion, whether it be a kit, or you acquire your own parts to do the conversion.

There is a cnc lathe conversion kit on this page (about $4K).
http://www.microkinetics.com/convkit.htm
You have to scroll down quite a ways.
I got a lot of other hits with "cnc lathe conversion kits" on google. One place I worked we did a small lathe this way which was controlled by an Apple computer. It was good enough for teaching purpose but wouldn’t deliver usable parts. IE too much dimensional variation.
You might want to check the second hand machinery vendors. I think a lot of the older ones are becoming available.
References :
I would suggest reading this article,
"Beginner’s Guide to CNC Conversions," at
http://www.dakeng.com/CNCconvert.html
This will cover the basic elements that need to be included in a conversion, whether it be a kit, or you acquire your own parts to do the conversion.
References :
http://www.dakeng.com/CNCconvert.html