The guys at the LSE developed a cheap robot for olfactory swarming experiments the LSE miniQ!!! The aim was to create a robot as cheap as possible but still usable in swarming experiments. This was accomplished by starting with a DFRobot miniQ robot. The robot was hacked to support a e2v MiCS 5524 gas sensor and two LEDs on top. These LEDs are used for localization using a camera for correcting the bad odometry that results from the poor resolution on the miniQ optical encoders.
The LSE miniQ was designed from the ground up to work with ROS. All the software is free for download at http://www.ros.org/wiki/lse_miniq_robot.