One of the common CAD programs I keep hearing mentioned is Rhino. According to Wikipedia Rhino was originally a closed-source open beta and there is still a very active development group. There is also an active support forum for the latest release, Rhino V5.
McNeel North America owns and supports Rhino and has a helpful Rhino Wiki that covers most of the documentation for Rhino. As a company McNeel looks to “enrich its clients”, this directly from their main site:
For more than 10 years our focus has also been on developing and publishing specialty Windows software for designers, engineers, and fabricators, and their related support staff. Mission To enrich its clients, employees, suppliers, community, and stockholders – in that order.
The rest of these videos can be found on the Rhino Tutorials account on Vimeo.
With other systems coming in at $5k, Rhino offers a nice alternative to learn the basics. If upgrading to the full version after the initial 25 saves the published price for Rhino is just under $1000. That makes it reasonably priced when it comes to CAD systems.