As mentioned below, (or above i guess) it really depends on what you plan on teaching. If it's at ALL going to involve 3D, i would advocate for the free SketchUp software from Trimble.
AutoCAD is a dinosaur. It was great back in the 80s when it was really the only game in town (and its floating point calcs and precision were unbeatable). But now, 3D is the new game in town and AutoCAD just isn't great for it. It's why Autodesk has an entire library of applications with a much more intuitive 3D engine and interface (Revit, Inventor, ReCap...)
My guess is that AutoCAD is only kept around because of the number of users, but I'm guessing that those users are probably steeped in simple 2D drawings else they would have migrated to something more powerful like Revit.
All of this is to also say that most Autodesk products are relatively expensive. If your'e tied to Autodesk, you might check out ReMake - I haven't followed them lately, but they used to have free applications like 123D Catch and some others that i believe have been rolled into the Memento project and renamed "ReMake". Not sure if it's still free...
But I really think SketchUp might be worth looking at (it also has a pretty large community so help and tutorials abound).
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"Aah, there's nothing more exciting than science. You get all the fun of sitting still, being quiet, writing down numbers, paying attention...science has it all."