In Mexico you will probably find yourself earning well under US$1000, there are a jobs paying more but they are hard to come by unless you are pretty fluent in Spanish, have at least a Masters, and are lucky. Most jobs are paid by the hour, housing is almost never included, neither is the flight over there, for that reason you ill work once you're there, but very little on offer for overseas hiring. Realistically you should find something paying around US$5-6oo a month fairly easily.

In Central America the same thing applies, but in Guatemala or Honduras don't expect to make more than US$3-400 a month, unless you work several jobs. No housing, no transport, and probably no work visa in most places. Maybe slightly more in El Salvador, I can't imagine anyone wanting to work in Nicaragua, Costa Rica is very popular and therefore probably harder to find a job there. I think Panama pays the best for CA, but not sure how much.

If you just go to any of these countries you will find a job, but take enough cash to get yourself home and also to survive at least a month or two, even better three.

As for the ITTO course, I don't know it directly but have heard from posters in another teachers forum that it is legitimate.