How much did Paul's travels cost?

The Apostle Paul famously made an extensive series of missionary journeys around the eastern Mediterranean (in various company, and stopping off in some places for months or years, also getting shipwrecked at one point). These are described in Acts and in the letters. I am curious about the rough **financial cost** of these travels, in terms of the means of typical first-century people. Basically, how wealthy would you have to be in order to make these trips (assuming you're paying for it all yourself)? How much support might therefore have been required from other Christians in order to finance the voyages? I'm not after exact numbers - just an estimate of where these trips fall on the scale of "Paul could easily have paid for the whole thing out of his own money" to "this was a major outlay for the whole church community". [Image from Wikimedia Commons - JWooldridge CC-BY-SA](http://commons.wikimedia.org/wiki/File%3AMap13.jpg)