New York to Nice is roughly 3,460 nautical miles — a genuine transatlantic sector, and past the usable range of every heavy jet once passengers, baggage and reserves are aboard. Only an ultra-long-range aircraft makes it non-stop, in around eight hours eastbound and closer to nine coming back, because the jet stream helps in one direction and hinders in the other.
Private jet charter from New York to Nice starts from $104,500 on the smallest suitable aircraft. That is an indicative starting price, not a quote: the figure for your trip depends on which aircraft are available, where they are positioned and the date you fly.