This just applies to transport, not attack helicopters.
I just bought one, the Maverick. While I was saving up for one I was calling in the Merryweather Pickup (Accessible @lvl 30 iirc) that costs $1000 a go, and is delivered to your feet.
With the PAID for one that costs $780,000, not only does it STIL cost $1000 each time you use it, is only delivered to the nearest heli pad, making it actually less convenient than the Merryweather one.
Anyhoo, thought I'd warn other for five minutes before this thread disappears under a new wave of for/against farming threads