It cost me about £20.
All i bought were the servos (£7 each HS-311), IR LEDs(20p each), phototransistors(20p each), resistors (10 for 40p), quartz crystal oscillator(80p), prototyping board (£4) and capacitors(~£1).
The robot body was made using the case from an old floppy drive, the microcontoller was ordered from microchips sample site, i allready had a programmer (but these are really cheap to make), the wheels were made from cut out cardboard, battery from an old RC car... i think thats it.
Yeah its really cheap. I reckon its harder than the $50 robot though, since the microcontroller is just a chip. There is no board that it comes with so you have to sort out the oscillator, power, possibly UART all by yourself. I programmed mine in assembly which was an experience
but i recommend using a c compiler (PICC Lite or C18).
Ermmm yeah i think thats it