Sure, the mechanical components don't scale up. I wasn't referring to upscaling a toy drone. But, if - and it's an if until someone actually solves all the problems - someone comes up with an electric airframe that works well enough for personal transportation - then I think it's more likely than not to have economies of scale to kick in and drive the cost down together with commoditization of personal flight.
Sure, there are lot of if's there. But mainly my guess "an electric 'quadrocopter' will be cheaper for personal transport than helicopter" is based on two things:
* it will become popular, hence driving unit costs down
* the vehicle will be cheaper to operate than a combustion engine powered helicopter
I think there are two separate issues: electric vs. combustion, and quadrocopter vs. traditional helicopter.
> But mainly my guess "an electric 'quadrocopter' will be cheaper for personal transport than helicopter" is based on two things: * it will become popular, hence driving unit costs down
Why? Is this because of the electric part or the quadrocopter part and how does either make it more likely to be popular?
> * the vehicle will be cheaper to operate than a combustion engine powered helicopter
Again are you getting this from the electric aspect or the quad aspect, and what's the reasoning?
I don't know. I'm pretty sure lots of aeronautics engineers have an actual professional answer to this. I mainly hoped with my comment that someone that had actually ran the numbers could chime in.
Taneq's answer above sounds fairly credible so I'm probably wrong about this.
To gain a better intuitive understanding of the problem, consider why we can't use selective breeding to create a mouse the size of a horse.