The challenge was to keep the Arduino Robot Labs fee to $50. I found the following items on Ebay from Asia. I never thought I could do this, and it has not been done yet, but I have hope.
UNO R3 Kit - Starter to Ultimate - Arduino Compatible, LCD, Breadboard, Sensor $21.96
Motor Drive Shield Expansion Board L293D For Arduino $4.48
HC-SR04 Ultrasonic Module Range Distance Measure Transducer Sensor $1.96
2WD Motor Smart Robot Car Chassis Kit Speed Encoder Battery Box for Arduino 1:48 $13.27
Total $41.67 and this is with postage paid.