Blender with Hardops, Boxcutter & BoltFactory
Ondsel
Plasticity
Sverchok - parametric CAD tool for Blender
https://blenderartists.org/t/technical-drawing-tutorial/1548370
https://blenderartists.org/t/tutorial-2d-cad-drawings-with-blender/1550767
Essential 3D Print Farm Upgrades!
How to price
Not sure what 3d prints to sell?