Finding a new robot platform

Although I haven't yet completed my first version of SHORT-E built on the Scooterbot two-wheel platform, I have already started pondering about what my next robot will be like. As I wrote in my earlier post, the Scooterbot cannot really move on anything else than hard floor. We do have wooden floors in our apartment, but there are also rugs and thresholds that pose a big problem for SHORT-E.

Although I won't probably be getting a new platform at least for a few months, I've listed my (currently known) requirements and started to sketch a list of alternatives.

Here are my requirements:

• Tracked, four-wheeled, six-wheeled, or similar type that can move also on carpets and rugs, and overcome small thresholds and obstacles.
• Preferably available as an off-the-shelf kit, with chassis, wheels, motors, etc.
• Big enough to have room to mount a Chumby One in addition to batteries, an Arduino, web camera, sensors, etc.
• Possibility to mount a gripper or a robot arm.
• Preferably enough space inside the chassis for batteries, Arduino and a small breadboard or printed circuit board.
• Shouldn't cost more than 500€, and the cheaper the better.

My current list of alternatives is pretty short:

Traxster II

• Large enough, seems pretty rugged.
• Enough room inside for batteries and electronics.
• Good-sized surface to mount Chumby, camera, sensors, and gripper on. 
• Includes two DC motors but no batteries or electronics.
• Motors have integrated quadrature encoders, which is nice.
• Price: 192.55€ 

Lynxmotion Aluminum 4WD1 Rover

• Also large and rugged.
• Some room inside, at least for batteries.
• Specially designed add-ons and accessories available: gripper kit, extra decks, etc.
• Includes four DC motors but no batteries or electronics.
• Where to fit shaft encoders? The motors included do not seem to have rear shafts. Would perhaps have to buy different motors, which would add to the cost.
• Price: 235.43€

DFRobotShop Rover

• Small, but might be just large enough with the optional expansion plate.
• Comes complete with an Arduino Duemilanove. Although I already have one, it wouldn't hurt to have two (no need to butcher SHORT-E for parts).
• Comes with the Tamiya Twin Motor Gearbox and a DC motor controller for the Arduino. No rotary encoders, but I could probably install my CNY70 based ones. I found a good article on how to modify this gearbox for adding encoders.
• According to the user guide, Lynxmotion Little Grip should fit. Weight would have to be added to the rear, but this wouldn't be a problem - I have to put the Chumby somewhere. I'm more worried whether the robot would be powerful enough to carry everything.
• Perhaps too small for everything I want to install?
• Cheap, price is 89.99€

At the moment the Traxster II is the top contestant, although I do like the specially designed accessories available for the Lynxmotion 4WD1, and the low price of the DFRobotShop Rover plus the fact that it comes with an Arduino and a motor controller.

I would really appreciate comments or advice from other robot builders. I just started this blog a couple of days ago and I know the number of readers is still small (haven't even been properly indexed by Google yet), but maybe there's already someone out there.