Holding an Amex Delta Reserve card is the cheapest way for those without Delta elite status to gain unlimited access to Delta Sky Clubs whenever you fly with Delta (effective 2/1/25, Reserve card members will receive 10 visits per year to the Delta Sky Club and must spend $75,000 or more in total eligible purchases on the card to earn an unlimited number of visits each year going forward). However, The Platinum Card from American Express and The Business Platinum Card from American Express also offer Delta Sky Club access whenever you fly with Delta and carry your Platinum card.