Due to multiple factors, expect to potentially pay more when booking in December. For low rates, August can be a great choice for travel to Strasbourg. Flights to Strasbourg from New York LaGuardia Airport in August are about $971 on average during August, but can be found for as low as $488.
Regardless of the time of day you decide to fly, the ticket price will remain around the same. Book flights from New York LaGuardia Airport to Strasbourg as you normally would.