very expensive. you'd have to sign all kinds of forms. plus- you cant just hang out of a helicopter with a camera- like you as in an everyday normal person. what you COULD do is build your own helicopter...yeah....i'd do that.
http://www.coptervision.com/
They use a remote control helicopter to get the shots. I've seen clips from companies who do this and the technique works GREAT!
I took my 100A on a helicopter tour over the Grand Canyon. I encountered several problems. I had only owned the camera for less than a week. I stupidly had the shutter speed set to 1/24th. I was crammed up against the right side window as there were 5 other grown men and the pilot onboard, limiting my ability to frame the shot in the viewfinder or the LCD (assigned seating by weight). And most of the money shots were facing the sun, so everyone and their white t-shirts were reflecting off the windows. And distracted at the last minute of touchdown so I even missed that shot.
All told, I got about 2 minutes of useable footage out of a 25 minute ride.
But I am sure your question is specific to a location shoot, as mine was vacation footage. Carry on.