OK so this is on you to buy. My opinions, yes AutoCAD would be nice to have but it is expensive. I am lucky that I am able to use the full version along with Acad Arch and Revit but if I did not have these this is what I would do.
1. For drafting look at low and no-cost AutoCAD alternatives. BricsCAD is one and Draftsight (free but 2D only) is another.
2. 3D, well there is always Google SketchUp. I use it all the time and the Pro let's you import/export DWG files. There are ways around this with the free version.
3. Rendering, look at programs like Kerkythea for rendering your 3d SketchUp models.
Here is a shot of a CAD to SketchUp design I am working on at the moment.
Playing with a few options on a small house design. I have also used this combination for cabinet design in the past.
For some examples look at the link at the bottom of my posts