Unfortunately NY hotels all have deals with car services where the same car service that would charge you $100, will charge $200-250 if booked through the concierge. I use Elite which is considered high-end, but unfailingly as timely as anything in NY can be. If you have luggage, for an extra $15, the driver will meet you are baggage claim.

That said, there is nothing wrong with NY cabs --- they are plentiful at the airports and downtown hotels, take credit cards and as is noted elsewhere flat rate of $45 ($60 w. toll + tip) to/from JFK.