I've have been enammered with Boston Dynamic's robots since first seeing them more than 10 years but really starting thinking about making my own when inspired by James Bruton's OpenDog project on youtube. His project rationalized a few concepts that made the build feasible for me and I began thinking of how to make a quadruped robot but cost was my primary consideration. I had the time so I began designing and printing anything that I could. This resulted in picking a gear-motor and designing a recirculating ball screw actuator and printed bearings based on readily available and cheap 1/8" and 6mm balls.
More recently, I've run into an issue reliably reading my chosen mechanical encoder so I'm moving to AS5600 magnet encoders at each joint. While a bit of a cost impact, this should solve not only the noisy mechanical encoder but several other know issues.
Work In Progress at the moment but I'm actively working on the project and will post updates.