Burlington (BTV) is 1 hour and 30-45 minutes away has good service to all three NYC airports w/connections worldwide and both Washinton airports. Jet Blue flies into BTV.
Albany (ALB) is only 15 minutes further away than Burlington. It has more airlines and more flights, including Southwest Airlines. Albany Park-and-Fly will take car of your car, long or short term, have it warm and ready to go upon your return which is really nice in the winter. They handle your luggage. They’ll even wash your car and provide pet lodging.
Montreal (YUL) is an alternative to get non-stop flights to many cities in Europe but it is a 2.5 hour drive.
Plattsburgh (PBG) has a new passenger terminal and is served by three airlines. Penn Air, flies direct to/from Boston a few times a day in about 70 minutes. These flights make good west coast and international connections as well. The planes are 34 seat turboprops. Allegiant flies to Florida destinations. Spirit Air flies to Ft Lauderdale and has connections to Latin America and the Caribbean from there.
Charters from Lake Placid Airport
The Adirondack Flying Service is a charter service out of the Lake Placid Airport right near the Horse Show fields. They will go anywhere. Trips to places like Boston and New York City are common. You can get a price quote on their website.
The prices are per plane, not per person, and they can fly up to 7 people. So if you are a family or a group, it can be more competitive with commercial airline prices than you think. The airport is only 20 minutes from Keene, saving a lot of travel time. You get right on the plane without check-in, security, or boarding lines. I’ve used the service twice for day trips to Boston and to Hartford and it was great. They also do scenic flights around the area.