Firstly, genuine students get large* rebates on AutoCAD (however the student edition leaves watermarks in your cad files and on your drawings too, from what I remember).

Secondly, there is a time-limited trial version of AutoCAD available.

Thirdly, there are several cheap or free for personal use 2D CAD packages that work similarly enough to 2D AutoCAD that you won't be lost in it (google intellicad). They lack the advanced 2D and 3D modelling abilities and CAD-CAM integration of recent AutoCAD versions however, but they are perfectly adequate for draughting.

*For certain values of large, as defined using a dartboard at AutoDesk.