Suggestions for a small ground rover that runs ROS?

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I understand that this question might be somewhat out of scope here. But I hope that answers.ros.org is better than the mailing list. Please feel free to correct me otherwise.

Can you recommend a small ground rover which:

• has max dimension of within 1 foot (somewhere between small toy rovers and a Clearpath Husky)
• fairly light and easy to lift by hand (<6 kg)
• fairly cheap either to buy or to build (maybe around USD 600)
• is capable of navigating in fairly rough terrain (like rocks or swamp)
• has a well-known slip model for its wheels
• can either receive command velocities over a wireless link remotely or can physically support a netbook running ROS

I can't think of anything to tag this question with :-(