I took K2 on a glacier landing last summer. Our original date was cancelled on the morning of the flight - on our way up to Denali - due to weather and they booked us for a few days later on our return trip. It wasn't cheap, but it was amazing. We did use the Northern Lights coupon - 25% off, but I think you had to have 4 people minimum.
We did need a Denali pass, which is good for 7 days, or we would have had to pay the National Park entrance fee. $10pp - pretty insignificant in comparison to the cost of the flight. And I'm pretty sure they just asked if we had one and trusted us when we said yes.