If I were getting back into TESOL (not likely right now), I'd definitely get the master's first. Live and learn, man. I would also make sure I went with the absolute cheapest master's program I could find. I'm telling you, and I'm sure you already know this, that most schools overseas won't care if you get a master's from K-Mart TESOL or Harvard. I know your students sure as hell won't care. Showing up at most schools, high schools and Unis, with a high priced master's is as stupid as wearing your church-going tux to work in a slaughterhouse.

Yeah, go as cheap as you can and save that extra money for retirement. By a bond with the extra dough. You may need that to keep yourself out of a McDonald's mopping floors when you're 65.

You don't need to spend a lot to get an adequate master's degree.