This guy may be able to build a robot like that for $50, but he's obviously an analog wiz, and is being very optimistic with his pricing.
I also don't believe you could build with all the features he's talking about for that price, unless you build most of the components yourself (like for instance, he says you can use either non-geared motors, or build a gearbox yourself).
The difference between that page and what Admin is doing, is that anyone can build what Admin has described, if you have a soldering iron and a few basic tools.
- Jon