Due to multiple factors, expect to potentially pay more when booking in June. For low rates, September can be a great choice for travel to Kuala Lumpur. Flights to Kuala Lumpur from St. Louis in September are about $1,152 on average during September, but can be found for as low as $827.
Regardless of the time of day you decide to fly, the ticket price will remain around the same. Book flights from St. Louis to Kuala Lumpur as you normally would.