The commented kit is not being sold currently at dx, but it’s sold at Hobby King ]
There are also others kits like:
Funduino Tracking Maze Car for Arduino
Smart Car Chassis Kit for Arduino
I have bought the most affordable robotics platform (some photos here) I have found around Internet (at DX): 38€/49$ for all this components:
Arduino cheap robot car
It’s really cheap, all the components work flawlessly and very well but IT DOES NOT INCLUDE ANY DOCUMENTATION and some parts (pan tilt base) are impossible to ensemble (it needs another micro servo, 3€/4$) and there is no way to mount on the robot base. Even that, I Think is a good deal, but you should work to get all the needed information (yes, all needed information is over Internet) and put your imagination to build it. I have used Lego Technics parts to mount the ultrasonic sensor.
Here is all the info I have found for every electronic part, code examples and, of course, (soon) a video.
My Smart Car construction
[Update March 30, 2013: Added photo gallery]
I will start a C. C++, C# robotics programming Workshop/tutorial with the cheapest robotic platform I have found at dealextreme.com: (Arduino based) plus a Raspberry Pi (like this that use Bioloid as the hardware platform):
I have not still received the kit, but I will review the kit and start the workshop as soon as I receive it.
This is the first drive of the first version of an 6×6 rocker-bogie suspension inspired in Mars Curiosity rover. It has been built using a Bioloid Comprehensive/Premium kit plus a few parts.
A tougher test: