As far as I know, there is no programming solution that supports the RS485 port at present. RobotC does not currently provide access to the RS485 port. It's under consideration for 2007 development.
I looked up the AX servos and they have a TTL signal level. You probably meant the DX series of servos which have RS485 outputs. They are three times as expensive. The price I saw was almost $200 US each. See http://www.tribotix.com/Products/Roboti ... alogue.htm
. Are these the servos you want to use?
You might want to consider alternatives. For example, use standard NXT motors with their encoders. There are a couple of solutions for expanding the number of NXT motors supported. Would NXT motors fit your application?