Hydraulics are not necessary at all, graviman. The "power assist" could very well be electric, such electric jackscrew actuators are in normal use today on many aircraft, and they have the force to be used wherever pilot muscle power alone can be used to control an aircraft. these cost about $1500 apiece, so all four axies of control should be less than $10,000 cost including the computation. Simple inertial sensors are also quite cheap, when they are useful for stability only (Flight Quality vs Nav Quality Inertial Sensors). The entire cost for the auto fly could be 12000 today, at very low quantities, at high quantities, the cost could be down to $2000 or so.
Unmentioned by the stabilizer bar advocates is that the bar specifically ignores pilot input unless the input is held long enough. This means that mechanical stability systems almost always reduce plot controllability and control response as necessary costs of their use.
As I said before, I see no reason to make complex mechanical systems (stabilizer bars, dual rotors, specially designed flapping hinges, etc) to achieve ease of control and high stability.