The rather heavy and extensive prototype of a prosthetic arm appears to be affordable and allow for a wider functionality, being actually thought- or brain-controlled through a head set. This appears to be geared towards above rather than below elbow amputees.
There now is a video about this.
Their premises, however, are interesting. On the project page, we read:
Most artificial arms are controlled by muscles near the amputated limb, which can make the device slow and frustrating, whereas Bionik Labs built an arm themselves, using drills, a band saw and their own computer software that moves in response to brain signals.
"Most artificial arms" are body powered. They are not slow and frustrating to use. They are extremely fast and are an immediate type response prosthetic arm. Body powered arms are extremely functional and light weight compared to any other. However, one does need some residual limb left to operate a body powered arm.