$5 according to the YouTube documentary posted in your sibling comment.
$5 in 1977 is about $21.15 give or take a few cents according to most of the website i checked the numbers on.
So while it might be $5, that was definitely not as cheap as it might otherwise seem.
Regardless of the inflation adjustments, ~$20 is surprisingly inexpensive for a commuter helicopter ride, I wonder if the economies of scale really do bring it down or if they were still eating their losses trying to grow business at that price.
Taxi flat rate from Manhatten to JFK is over $50. How the price for a helicopter ride could be on the same order of magnitude as a taxi is beyond me.
An uber to JFK from Manhatten is ~$100 - that's still dirt cheap!