I used TurboCAD proffesionally around version 8.2 (professional), and would recommend it for r/c design, even going into 3d, it is fine. It is well setup for doing 2d sketching.

It really boils down to what you want to do, if you want simple 2d sketching , cheaply then , a second hand version of Turbocad is a very good choice if you want to get into 3d solid modelling then , doing this cheaply , is possible, Alibre design have a FREE download at the moment , of an express version of their software , (limited to 10 unique parts in an assembly), but still solid modelling for free. You can upgrade for $125 , I think to take this limit up to 30 parts and get access to further functions.

If you really do have the time to spend and would like some pukka designs , then yes I would go with the Proengineer personal edition (Full capability !!!), for $200 that a complete steal , but hangon a sec with buying it at the moment because I think I'm right in that they are about to bring out a new version (WF4).

Solid works did used to do a personal edition but I think they have stopped that now.

As for the Student and academic versions there is alot available on Jounrney Ed if you can wangle an academic license.

Nick