Cheaper solution to Dynamixel RX-64 continuous turn servo motor

Dear Robotics Experts,
I am looking for high torque continuous servo motors for a all-wheel drive mobile robotic platform. Total weight of the platform will be
approximately 30kg, including batteries.
This platform will be used for robotics experiment (not for game) and I want to be able to control all wheels accurately both in speed and position modes.
I've considered using geared DC motors with encoders, DC servo drivers and motion controllers. I've also considered using Dynamixel RX-64 continuous turn servo motors which can be daisy chained and all motors can be controlled with a single RS485 line. This is an easy solution but an expensive. Because as you can see on the following URLs Dynamixel RX-64 is expensive.
http://www.robotshop.ca/home/suppliers/robotis-en/robotis-rx-64-serial-servo.html http://www.tribotix.com/Products/Robotis/Products.htm
Do you know any better (lower cost) solution? Is there any cheaper alternative to Dynamixel RX-64 ?
Merci,
Roberto
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http://www.robotshop.ca/home/suppliers/robotis-en/robotis-rx-64-serial-servo.html
Have you considered stepper motors and something like a Phidgets controller ? http://www.phidgets.com/products.php?product_id 62 Sounds like it might be a good fit.
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Roberto,
DC Gearmotors with encoders sounds like the better and less expensive option, but I'm not sure what you mean by "position modes". Have you determined the speed requirements, battery voltage and the drive train design? Direct driving of each wheel should be possible, making the drive train simpler to build. If you want to move the motors in steps like 1/4 turn, the stepper motor approach would be more appropriate.
Take a look at Pololu's motor controllers - http://www.pololu.com/catalog/category/10 .
Eddy Wright Wright Hobbies Robotics
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