yeah, I've seen $30 for a day pass for your guest when you've got a fancy membership, and Delta day-pass rates tend to be closer to $50 (similar to the rates they have here -- https://www.delta.com/skyclub/purchasemembership_performRequ... -- but you need to buy it associated with a ticket somehow so the only rates listed are bulk rates).

You can also buy the membership, or apply for the credit card that gets you the membership as a miscellaneous benefit.