Continental Airlines is the only airline I know that has cooled and heated area for the pets to ride. The others operate like Goldenkitty mentions, and no they are not air-conditioned. We have used Delta in Spring and Fall, the flights were all early in the morning.
Last year, all flights one way for a kitten to ship out in the cargo area, were all $170, it didn't matter which airline was called, but I would assume the rates change frequently. I haven't shipped any kittens this year.
There is a big variant in what vets charge for the health certificate.
Here is a link to Continental, it may have information you are looking for.http://www.continental.com/travel/po...ault.asp&SS=CR
I also agree with Goldenkitty, I don't like to give rabies earlier than 4-6 months of age.