https://www.transfermarkt.com/-what-is-the-cheapest-day-to-buy-flights-on-united-/thread/forum/696/thread_id/49747/page/1#anchor_47325
https://www.transfermarkt.com/-what-is-the-cheapest-day-to-buy-flights-on-united-/thread/forum/696/thread_id/49747/page/1#anchor_47325