The Chase Sapphire Reserve comes with Priority Pass access. Most of our base airports will have some sort of PP perk, even if it's not a lounge. For example, at IND, you get $28 off your tab at the bar/grill at the end of the B concourse. I've had it since before I was flying, and it's been a good card.
Annual fee is $450, but it reimburses $300 for any "travel" related expense, making the effective annual fee $150. You can also use it for Global Entry/PreCheck every 4 years, on yourself or someone else, as I recall.
The Amex Platinum is another good card. It's fee is $550, but also comes with $200 worth of Uber rides, a $200 airline fee reimbursement, along with Delta Sky Club, their own Centurion Lounges (which are great), as well as Priority Pass.
The bottom line, don't let the annual fees scare you. Yes, it's a bit of a shock when you get it all in a lump sum one month out of the year, but you're saving money during the course of the year with the cards almost enough to offset them.
Airline-specific lounges cost a lot, and have increasingly been putting restrictions on when you can get in.
Even though the lounges often aren't quite as nice, the Priority Pass network is pretty great, and it's extremely global. You can find at least one PP lounge in just about every major airport in the world - perfect for layovers when traveling for fun.