Next step for hobby CNC

What I would like to build is a home shop welding robot. The one
thing missing is the ability to run a program by "teaching".

All the MIG robots I have seen work this way. You switch the machine
to "Teach Mode" and manually move the welding head around the work in
whatever path you need. While you are doing this the computer records
the motion and translates into G-code. You have simple record, pause,
rewind, etc.

I pictured building this with steppers with encoder feedback. The
"recording" program and the control dont' even have to be related.
There's no reason CNCpro (or other hobby controller) couldn't run a 3
or 4 axis robot arm. The problem right now is on the software side.
The Gecko G201's already have the free spooling feature built in which
would make it very easy to switch back and fourth from teach to run
modes.

Does anyone know of any software (free or cheap) that will perform
this "recording" function as I have described? Are there some details
that I am missing?