I think you're going to have a difficult time finding any domestic airline willing to accept turtles in the cabin. It's incredibly stupid since they're even more harmless than cats or dogs but it is what it is. We're talking about a slider turtle not a snapping turtle.
I hate to suggest this but what about shipping the turtle via UPS or FedEx? This is how I understand commercial shippers ship turtles. Here is a page on how to ship turtles:
http://turtlerescues.com/shipping_turtles.htm It kind of kills me to have to talk about shipping any animal. I would drive if I had the time.