Wow, that's certainly dissuasive.
By the way, are there some kind of autopilots on modern amateur planes? Or is that even possible to integrate any ?
By "amateur planes" do you mean ultralights or experimental homebuilts? The answer depends on which -- an ultralight could hardly tolerate the extra weight that a decent autopilot would require. And most experimental homebuilt owners probably want the pleasure of actually flying their planes.
Autopilots are more attractive to people who fly long distances and not for pleasure. I had a Mooney 201 years ago that I would fly on business, and the flights tended to be long and a bit boring, so I had an autopilot installed.
Picture of me putting my bicycle in the backseat of my Mooney: http://i.imgur.com/R5qVo.jpg
Where does most of the weight come from in an autopilot?
On all small aircraft (and some larger older ones, DC-3s for instance), muscle is the only thing that moves the control surfaces. They're very well designed and counterweighted so that the required effort is quite minimal.
At 254 pounds you want light and simple. FBW requires actuators. And controllers. And sensors. And power. And then you have to double up everything for redundancy. You would easily eat up 50 lbs or more making a reliable FBW system and it would cost 3-4x what the entire aircraft cost.
Even with normal light aircraft a FBW system is both unneeded and overly complex. Cables and pulleys are extremely reliable. They are inspected every year (along with the engine and various other pieces of the aircraft).
(I don't fly and know nothing about this but it sounds pretty cool)
Really helps when flying in congested airspace or while performing 'complex' arrivals.