I had make this $50 robot (although it actually cost me more like $180 total), I'm using Arduino-compatible bootloader (so that I can use the Arduino IDE to program), It consists of a ATmega168, a 16Mhz resonator and a 10KOhm pull-up resistor for the reset pin. Continuous Rotation Servo, SRF05 Low Cost Ultrasonic Range Finder and CD-ROM as the base to make this Obstacle Avoiding Robot with holonomicwheels.