[AndreyErmakov]

As a rule, never travel to a job interview on your own expenses, unless it's just a few USD/EUR for a local bus/train ticket or something similar. That would demonstrate to them that you don't value your time and money and that they can potentially abuse you further down the road. You will also encourage them to continue with that strategy in the future.

As for the red flags, google the names of the people who you will be working with and also of those who manage the organization. Go through their public activities and get an idea of their personalities. Sometimes you will find out that your potential colleagues are real jerks, and it can happen that the organization (especially if it's a startup) is run by a 24-year-old arrogant kid. In both cases I would skip that "opportunity" and would look for something else.

[kevindeasis]

I agree, in a way it kind of is a bad precedent.

That second advice is gold. I've been doing it since day one and it definitely helped to paint a picture the type of culture a company has. Luckily, most of the people that have been interviewing me seem like genuinely nice folks.