Due to multiple factors, expect to potentially pay more when booking in December. For low rates, July can be a great choice for travel to Aruba. Flights to Aruba from El Salvador in July are about $625 on average during July, but can be found for as low as $438.
Regardless of the time of day you decide to fly, the ticket price will remain around the same. Book flights from El Salvador to Aruba as you normally would.