Actually...he's right...it's a FAR drive for a taxi and I'm sure they won't do it. It'll cost you an arm and a leg...or two!
Going from ISP to Manhattan...is really an adventure...
Shuttle or taxi to the Long Island Railroad Station in Ronkonkoma (make sure you take the right line) to transfer to the subway you need to take. It is an hour-two ride.
Good luck!!!