I think not going to the delta interview because you don't want to pay 300 or even 800$ for interview prep/gouge is shortsighted.
you'll make that back in 1 month of your delta company sponsored 401k. Waiting to make captain at 15 at SWA will cost you a lot more than 300$.
We all have our reasons for picking the airline we want, but don't put a bullet in your career over 300$.