Background: I own the latest Geomagic Design at home and use current Autodesk products at work.
If you have in decent internet connection Autodesk has several free options online.
https://www.autocad360.com/ http://www.123dapp.com/design
Draftsight is pretty close to AutoCad and works for those of us who still type commands. The constant emails got old for me so I stopped using it.
I also found
http://intellicadms.com/site/cms-intellicad-products.html and have not used it yet but looks decent for around $100. Uses all Autocad commands and is .dwg direct compatible according to the site. Considering this for simple 2d drawings in the shop to load into cam software.
Most 3d cad packages are parametric modeling so everything works on constraints which I don't like for 2d. "Drawing" in a 3d cad package is generally the printable output with dimensions from the 3d model.
Geomagic Design (formerly Alibre) is 1/3 the price of Inventor with much of the same functionality. Fairly easy to use as parametric cad, outputs to .dxf .dwg .iges and .step.
Note: Cubify invent (from the same company) is not drafting software it is made to create parts for 3d printers. There is no 2d output or dimensioning.
Freecad is a 3d parametric modeler which is, as the name implies, free. I found the learning curve to be a little steeper than Geomagic Design (coming from Inventor and Mechanical Desktop) but you can pay in hours instead of dollars. Time spent learning this package will largely carry over to several industrial cad packages.
Sketchup. NOT associated with Google anymore. NOT really free (for full use). NOT really cad. I would suggest against anyone who is not doing architectural design work from spending any time trying to learn this. Any time spent learning sketchup will not help you operate any cad system that I have ever used (I have not used them all by any stretch). I would consider it closer to Cubify invent. Sketchup requires you to pay to output .stl (3d printer format)
As with all things on the internet YMMV but hopefully this info is somewhat helpful to at lest one person.