Is it ethically correct for me to travel to an all-expense paid job interview, including flights, if a pre-condition is my willingness to relocate for the job and at the moment I really don’t want to move, but if the offer and workplace are lucrative enough I might change my mind?
Quite a sensitive question. I would say that if you are open to accepting a job offer that is attractive enough - although you are really without desire to relocate right now - it would be permitted to accept the offer to check things out. Who knows what may transpire that may affect a change in your perspective and decision?
However, if your conscience feels uncomfortable with this approach, perhaps you can tell them of your reservations about relocating and let them make the decision as to whether it is still worth their while to spend their resources on "courting" you for the job. I don't think it is required to tell them this according to the strict letter of the law, but it is admirable to go beyond the letter of the law and act in the most ethical and moral way possible.
I wish you much happiness and success - and please feel free to write again anytime.