Speaking of autodesk and free... Autodesk has almost all of their software available for free through their student site. So those of us that are students can register and download. I use Inventor for all of my projects it's a fantastic program and is very very powerful (you can output 3d renderings like barts with a few clicks).
It is the educational version but I have never been able to tell the difference I think its suppose to put "educational version" on all drawing but I have never had an issue.
Autodesk student site:
Link