Eerrrm... just to clear up this little rumour about CELTA or Trinity certTESOL being for those who wish to make a career out of TEFL... it's not true at all. These are entry level courses which are very quick to do and are designed to give people the basics in teaching English, even if you're only looking to teach for a year.
They're good courses mainly because of the practical element involved, so they're a lot better than most of the online courses. A teaching course without actual teaching practice isn't logical for someone with no experience and would be a waste of your time and money. I can understand that these courses are considered expensive but they're cheap compared to other professions.
My advice? Do a CELTA, Trinity certTESOL or any course which has a decent amount of teaching practice as this is the only kind of preparation that is worthwhile.