i think you should pay if it's a plain ticket - he should buy the fancy one

I don't think there are any hard, fast rules on this...
depends on a lot of factors - who has some spare $, who can travel easier, more flexible schedules, what's the destination - if you have the choice of a really cool place vs. a 'plain ole' one, etc.

I once flew, at my own expense by choice, to meet someone. It was 'last minute', my schedule was more flexible, he would have had to find a pet sitter and doesn't like to fly, he had a couple hour commitment over the time I was to be there that was not breakable, I could take time off work at the last minute, etc. so I went there. He paid for most everything while I was there, groceries, meals out, etc. Not that I expected that at all, he just did.

No rules for me, just whatever works at the time for the two individuals involved...

If you want to meet the guy. That is your choice.Pay for it.

If you both like each other and both want to see each other, why not split the expenses?