I can't say enough good things about the new all stryrene plans that the R2 Builders Club has put together. I have built an aluminum/wood droid, and have started working on my second one in styrene. The styrene droids are surpisingly strong and capable. You really aren't sacrificing much, and the benefits are huge.
You can have a full sized, fully functional, club spec droid for much less than was possible in the past. All the parts can be build with basic tools... all you need is time.
There are even laser cut styrene R2 domes now.
Check out
www.Astromech.net and good luck!