Gibbscam software

I am looking for a software package similar to GibbsCam for use in a
high school shop class, but without the high cost. I have tried BoBCad
V18 however it is difficult to use and does not allow 3D modeling. Any
suggestions? I have my students design in Rhino 3D...I need a package
that coverts STL and IGS files into G codes and illustrates results
in 3D. MillWizard works, but has too many limitations.

Thanks Dennis