Need advice what I should buy

Hi im a newbie and I need help with which part I should buy to make a robot that can go by itself and watch out from walls and stuff (almost like a robot vacuum cleaner without the vacuum part) it’ll have 4 wheels but capable later with tracks and it has to have at least 2 sensors and 1-2 servos. I wonder if anyone can recommend any good but cheap parts like which microcontroller, motors(not too fast), motor controller, battery and sensor I should use. /thanks

You need all the basics of a robot; consider the Parallax Boe-Bot for Arduino, which has a track kit add-on. If a kit was not made for tracks, it’s very difficult to add them later. Browse the RobotShop website to see what kits are available. If you are looking to make a custom robot, we suggest following the Grand Tutorial Series to see what it takes to build a robot.