The cheapest is to strap things onto a 3 axis 3d printer. They can be had for < $200, which is much less than you could ever build one for. Beyond that, it's D

The cheapest is to strap things onto a 3 axis 3d printer. They can be had for < $200, which is much less than you could ever build one for. Beyond that, it's DIY, with a set of strong servos and a few budget microcontrollers/motor controllers, from Alibaba, and...a 3d printer to manufacture the rest, for something like an arm.