for each group:

amazon.com
arduino UNO: $19
USB cable: $4


sparkfun.com

for each group:
1 - $35.95 - SEN-11072 - IMU Analog Combo Board - 5 Degrees of Freedom IDG500/ADXL335
2 - $25.90 - ROB-08913 - Mini Metal Gearmotor 24:1  ($12.95 ea.)
1 - $9.95 - ROB-10077 - Wheel 90x10mm Pair - Black
1 - $29.95 - RTL-09896 - Ardumoto - Motor Driver Shield Retail
1 - $1.95 - PRT-00552 - Battery Holder - 4xAA Square
1 - $1.95 - PRT-10218 - 9 Volt Alkaline Battery
1 - $2.95 - PRT-09518 - 9V to Barrel Jack Adapter


for instructor:
1 - $14.95 - TOL-09141 - Digital Multimeter
1 - $9.95 - TOL-09507 - Soldering Iron - 30W US 3-Prong 110V
1 - $5.95 - TOL-09477 - Soldering Iron Stand
1 - $16.95 - TOL-08775 - Solder Wick #2 25ft. - TechSpray
1 - $1.95 - TOL-08793 - Needle Nose Pliers
1 - $1.95 - TOL-08794 - Diagonal Cutters
1 - $4.95 - TOL-08696 - Wire Strippers 30AWG
1 - $1.95 - TOL-09200 - Hobby Knife
1 - $2.50 - PRT-08023 - Hook-up Wire - Red
1 - $2.50 - PRT-08022 - Hook-up Wire - Black

alternative motor driver (cheaper, but you need to solder it together!)
adafruit.com
1 - $19.50 - Adafruit Motor/Stepper/Servo Shield for Arduino kit (v1.0) [ID:81]


If you want to make it run on a lithium-ion battery (cheap and light):

sparkfun.com
1 - $9.95 - PRT-10401 - LiPo Charger Basic - Mini-USB
1 - $0.95 - PRT-08671 - Jumper Wire - JST Black Blue
1 - $0.95 - PRT-08670 - Jumper Wire - JST Black Red

amazon.com
2 - $6.00 - LG Lithium-Ion battery 3.7V for AX275 AX300 UX300 AX380 WAVE ( LGIP-420A )