Are you English and buying with pounds? If so, then American duty free will be significantly cheaper for you because of the exchange rate.Keep in mind, however, that tobacco varies in flavor from region to region, even if it s the same brand and blend.I can t answer the question as to actual cost, sorry.
New York should be by far. It may be duty free in Heathrow, but it s cheaper with taxes in the States. One of the reasons most people here seem to smoke tobacco that comes in from Poland. Spain, France, USA or elsewhere.
Quit smoking in April 09 nevertheless bought 3 cartons of Kool 100s in December 08 at JFK for $62 in a buy two get one free deal.
To be honest, I dont want it, even if they are giving it away!