Hard to say without being there. The only time there's a chance to know is when there are trees & etc. in the shot. And from memory of actual sizes of helicopters. And of course the camera lens and sensor play a role as well so any guesses are even worse than the guesser might think. Not to mention everyone's memory of what altitude "really" is a certain height.
Given what it "looks" like though, to try and answer the question, I would say about 400'.