Is there a difference in the Helicopter power needed to stay on different altitudes? I heard that what can make a helicopter go higher is the presence of "Air" to power its engine.
Let's assume that the amount air would be exactly the same at different altitudes, would the power needed by the helicopter to stay stationary at 50 meters high be less than the power needed to be stationary at 200 meters (or even higher), or would it be the same?
 A: This is just an educated guess from an occasional pilot.
Let's forget about less engine air by making it an electric motor. Then the question is, is more power (wattage, horsepower) required at higher altitude? My sense is, it should be about the same, because the lift/drag ratio should be about the same. The rotor blades would have to spin faster to move the same amount of air, just as a high-altitude airplane flies faster to get the same lift. Then you come up against the speed of sound, but that's a different issue.
A: 
I heard that what can make a helicopter go higher is the presence of
  "Air" to power its engine.

The helicopter's engine is powered by burning fuel together with oxygen from the air, then its propeller forces air (not necessarily the same air which is burnt with the fuel) downwards to lift the helicopter upwards.

Let's assume that the amount air would be exactly the same at
  different altitudes, would the power needed by the helicopter to stay
  stationary at 50 meters high be less than the power needed to be
  stationary at 200 meters (or even higher), or would it be the same?

Yes, it should be basically the same if the air density is the same. Air density is not the same at high altitudes like one or two kilometres, but it's approximately the same from 50 metres to 200 metres above ground. 
Something called "ground effect", an improvement in performance, occurs within one radius of the blades from the ground. However, helicopter blades don't come as large as fifty metres. Apparently (from searching the web), the largest helicopter in the world is the Mil V-12, which has blades of radius only seventeen metres.
A: In your comment you wrote

I just want to know if it has to spend more energy to stay at different altitudes, not to flight from one altitude to another.

To get a solution for questions with varying parameters it is always advised to set the parameters to extreme numbers. Let's try to do this for your question.


*

*We suppose the density of air at any altitude to be a cnstant number. In this case the varying parameter is the gravitational pull on the helicopter and this pull will be decreasing with higher altitude. Hence the power needed by the helicopter to stay stationary at 50 meters high will be higher than the power needed to be stationary at 200 meters.

*We take in account that the earth's atmosphere is no more existant at approx. 200 km abouth the ground. A helicopter need this air to have an aerodynamical lift. Hence for a first considaration the power needed by the helicopter to stay stationary at 50 meters high will be lower than the power needed to be stationary at 200 meters.

*We take in account that not only the ensity of air decreases with hight but also the amount of availible oxygen. A helicopter need this oxygen to burn fuel to power the engine. Hence the conclusion is like for the second point.


BUT with the point 2 and 3 a avionic engineer may be will not agree. The helicopters engine and the rotor blades may be optimized for an altitude of 1,000 m. So this is a good example to memorize that physical models are often some idealizations and not as complex as the real life.
So the answer in German would be "jein" which is a unification of ja (yes) and nein (no). :-)
