When my brother was ill the American Cancer Society gave us a number to call at Southwest Airlines to get medical passes for my brother to fly to and from treatment. I had already called this airline and other and had been given discounts, but this was for free round trip tickets for the cancer patient and a caregiver. (so 6 round trip flights in all). I would be happy to share that phone number if anyone can use this service - I know they are a regional airline but there may be some in other airlines who offer the same type of service. (Contact your American Cancer Society - they have contacts the rest of us don't) I think they called it a "green pass". It is NOT standby - it is a must fly and I think you have to know 2 weeks in advance, but it works well if you are having to fly to doctor appointments. You can also change the day and time if you need too. They just sent us the tickets in the mail and we would call and give them the numbers when we were ready to use them. Your doctor also has to fax a letter saying you are being treated for cancer and are able to fly. (not on a breathing machine or something). I also found them very willing to change flight times if I purchased the internet specials (they don't usually do this, but make exceptions for those receiving medical treatment). They were so helpful and kind.
The free flights helped my brother and his wife so much financially and took a lot of worry off his shoulders.
I'm sure you are aware, but hotels will also offer medical discounts (sometimes up to 50%) if you let them know you are there for medical treatment. I just thought these avenues of assistance might help someone out there.