High-Precision Switch-Pressing Arm

I am putting together a compact robotic arm that will live on a benchtop and repeatedly toggle small mechanical switches at set intervals. Every actuation has to be reliable and repeatable, so the positioning accuracy must sit in the high-precision range (fractions of a millimetre, minimal backlash)... (Budget: $15 - $25 USD, Jobs: Arduino, CAD / SolidWorks, Electrical Engineering, Electronics, Mechanical Engineering, Mechatronics, Microcontroller, Motor Control, Product Design, Robotics)