CreditsTrainDepotControllerIncluded Scenery
      200Speaker  500CPU  100Servo
      35090 sec Voice Recorder  500Memory    
        50Voice Chip      
      2002 Servos (Engine)      
        50Reed Switch      
         50Electromagnet      
       500CPU      
    140010000100

Total credits used: 2500
All other credits go to the amount of plastic used.

Now, you may think that I need a pressure switch or an accelerometer. A button makes a good pressure switch for high sudden pressures, and since all velocity information goes through a CPU, it could calculate the acceleration.