^ If someone billed me first class flights after the fact, that would definitely be a problem. If someone asked for first class flights before the fact, that would make me think twice, but I would not exclude the possibility without considering all the factors.
As to Jesus and the others not asking for money, that is true, but they were supported. They ate, they slept, they were hosted in people's houses, etc. Paul worked a secular job, but clearly did not expect all those in ministry to work secular jobs (see 1 Timothy 5:17-18 in particular, in the context of the rest of 5 - widows are to be honoured, but elders are worthy of double honour).
I think there was a first century distinction between an apostle and an elder or prophet, and apostle being itinerant and the other two being resident. However, quite how far we should maintain this distinction depends very much on what you think about the special status of apostles in the immediate wake of Christ. Most preachers, however, are part of a local church, unlike Paul - I'm not sure of any examples of the Pauline style apostle today.
The reality is you have to take these things on a case by case basis. I would always try to make evangelistic events free, but I think the church should be willing to put their money where their mouth is and support all workers in Christ as much as possible.
Some here try to make out that those in ministry should not be paid for their ministry work, which is wrong, unbiblical, and simply not pragmatic. If you make a pastor have to have a full time job to support a family, they will serve you less. It's that simple. Why would you not prefer to support someone who can devote themselves full time to preaching the word and leading a church in service?