In level 41, General Corrosive, get to the upper ledge around the level via one of the bridges from the central hub. Go clockwise around the level until you reach the area with two "elevators" that do not go low enough for you to double-jump onto them from the lower ledge. Ride the left elevator up to the top. In a small alcove next to you, you will see the barter droids. The chip they sell is worth 150 washers. Keep that in mind before you enter the level.