[MrWild]

Well, I think you are half way there already. If you have a mill, and I'm assuming a used Knee mill, you already have a ridged quill and powerful enough motor to run it. I've been turning over in my mind a quick and simple 2.5D CNC mill. Forget buying ball screws and big motors to convert your mill. Forget buying a X2 or X3. Buy a mill/drill table and install some quality Acme lead screws in it. With an X/Y table CNC'd you can move the quill or knee of your mill for your Z and do 95% of what everyone else is doing with their full court press of X, Y, and Z. Early NC mills often had just two axis CNC’d with a manual Z.

The lathe and mill you have on hand can do a bang up job of CNCing the mill/drill table and except for the lead screws they come with, they are sturdy enough for many operations. You could be into a CNC mill for under $400 if you don’t mind doing your Z axis manually.

$120 mill/drill table
$80 for two stepper motors
$55 for lead screws and nuts
$80 for the drivers
$65 for bearings, couplers etc.
Use EMC2 for a free controller program, and a junk computer to run it on.
For a power supply you can either rewind an old microwave transformer, or gang two computer power supplies. There are stickies in the General Electronics forum on these two low buck options.

I’m sure you have the odds and ends scrap for making motor mounts and lead nut mounts. You don’t have to spend an arm and a leg to get your foot in the door. While $400 might seem like a lot to someone testing the waters, it is about the best bang for the buck you can have if you already have a manual knee mill on hand.