There has to be a big difference between what it would cost you to go to their interview and what the airline would pay for you - tickets on their own service or ID tickets on a codeshare/arrangement if they have one, crew rates for Hotac, etc. Whatever about covering all your costs, surely if the airline aren't arsed in assisting and making it cheaper for you by booking you into a hotel at crew rates minimum, what does that tell you about them? If the costs to you are small, suck it up if you want the job - if they're large, you're hardly being cheeky asking them if they can get you an ID ticket or book the hotel for you at their reduced rates?
Equally, anyone who insists on business class tickets and 5 star Hotac to do an interview is living on another planet, unless they're very valuable or flying a hell of a long way or doing an interview in a not-so-nice country.