Paying to go to the assessment is to get rid the people who go into the aviation industry just for money (like you)...
I don't think that is what Brad meant... He mentions he is in a well paying job at the moment, so it is only natural to consider the wage if you are thinking about switching careers.
You can be as passionate as you want, if the job doesn't pay the bills for a lifestyle that you can lead with your current career, that is a thing to think hard about.
I can offer no answers for the questions, but I have always thought it is absolutely ridiculous to charge an applicant money for an interview. You either want them or not. But the supply of idiots/hopefuls is big enough that they can get away with it I guess.