Forget the round rails and bearings.
I tried it circa 2006..

Steel frames, sand for smoothness / non-binding,
increase section sizes 2-5x,
glue in with industrial goops and bolt if you want, ..

For accuracy, a steel or granite machinists reference edge/plate, vertex 1000 mm is cheap to 0.04 mm / m,
sand with wide belt sander to remove most of the bend/curve.
Then assemble/build, with non-binding free-running linear guides.

You probably cannot make a good commercial-level cnc router for cheap --
no-one can.
Look at mechmate. 8-10k for parts.
I will likely make one for a local business for full-sheet 2.5 x 2 m size .. and will charge 20k€ or so.
It MUST have a toolchanger to be useful/profitable.
Likely, it will be horizontal, like the more productive modern CNC machining centers.

Most likely, the 20k€ cost is paid in 1-2 months.