traveling w your dog, help

I know there's certain papers I need from the vet, tags but just any past experiences would help. Because anything I've found online says each airport is different? My aunt said if we get a paper saying my dog is for anxiety she'll ride on my lap on the plane for free? I got her to be a special needs dog for me because I'm anemic/pre diabetic, but was told any special needs animal is super expensive and I just haven't got that kind of money yet and now don't know if I will ever. I was told it would be thousands. Anyway..