Last night I came up with a solution for a lightweight, but inexpensive robot arm for CheapBots. The arm is 0.6 inches wide and 5 inches long. Its grasper will be switched for an electromagnet. A relay will control the current for the magnet since the robot controller cannot provide that level of current. The arm will be light enough that a small servo can raise and lower it. The servo and arm will be turned on side, but a second servo could be mounted below to allow the arm to rotate about the horizontal plain.
I'm looking into hall effect sensors now as a way for the robot to detect the presence of a magnetic field. That should help the robot align its arm, because the objects it will pick up will be ping pong balls with small neo magnets glued inside (the bottom of the ball will have a cut hole so it doesn't roll).
Perhaps I can shoot the PCB for the arm tomorrow.