most of the things u will get readymade but then u will miss the enjoyment of making things ur self you will require
1) two DC gear motors of around 100 RPM
2) pair of IR sensors
3) any micro controller and motor driver L293D
4) battery 6 V or 9 V
5) robo chesis
6) 3 to 4 medium size wheels
total cost around 500 to 800 rs