Parts List 

All prices are in USD.

From Radio Shack:

Sentinel RC Tank              60-4257            29.97 (on sale)
        or
Chassis Assembly              12287694           14.99
Track (pair)                  12288213            2.69
Battery Pack Cover            12259008            1.99

6V Ni-MH Battery              23-0338            19.99
Battery Charger               23-0327            12.99  

From Acroname:

BrainStem by Acroname         S1-GP-BRD          79.00
BrainStem Interface Cable     S6-BS-WIN-CBL      32.00
UVTron Flame Detector         R67-UVTRON         65.00
Modified Servos (2 each)      R53-MX-400-CONT    39.80
Sharp GP2D02 IR Ranger        R19-IR02           21.00
Sharp GP2D12 IR Detector      R48-IR2            13.50
Polaroid Sonar Ranging Pkg.   R14-SONAR1         46.00

From a local surplus store:

200Mb Laptop Hard Drive                          10.00
Laptop HDD to IDE adapter                        14.99