No prewar rangefinder is better built and faster to use than a Leica III with a SBOOI (for 50mm) or SBLOO (for 35mm) mounted. The Leica III is the strongest, but also smoothest and best built camera there is and is a much more practical camera than a Contax. And as a bonus it is by far the cheapest Leica in black paint too.
Compared to a Leica III a Leica IIIc is a toy. It is as if you compare a Land Rover with a 2CV.
I have two of them: one I got for free and the other was EUR 165 if I remember well.