Actually you don't always get what you pay for and, as an experienced ESOL practitioner, having looked through a lot of course materials, some costing hundreds of pounds and others costing £50, there are some terrible courses out there. I also feel that, without any face to face experience, how can a purely online course prepare you for the classroom?
We offer a weekend TEFL course which I would consider to be an introduction to all aspects concerning teaching second language learners, which we then partner up with an online course with our agent, who will then take on the role of placing you in a teaching role abroad.
Due to the current climate and the glut of cheap courses around we're offering our weekend course for £100 and although I'm sure you can find cheaper ones, beware of purely online studies. There's also the point that many countries now are insisting that a proportion of the preparation studies for potential teachers must have been done face-to-face and, if possible, with some classroom experience.
The beauty of us is that we are also an ESOL school so we can offer you some practical experience in a classroom with actual learners.
Think about it very carefully. Lots of people are out to make a bit of easy money and not everything offered - whether expensive or cheap - is going to be of use to you.