using a stepper motor as an input device

I am new to this field - i have a programming background however.

I am interested in building a cnc router that i can use to do some
reverse engineering. I want to be able to trace and part (OK - for
now lets just say it's in 2D) and create a set of X-Y points.

Is this something that is commonly done? I know i could buy a
microscribe for $4,000, but i thought i could make something for much
less.

I would appreciate any comments or suggestions.