I did the one month program last year for about US$1,500. (Inflation's pretty bad, huh?)
The positives with my program were that I had never taught before and by the time I got my certificate, I had taught 8 practice classes. And I had watched some classmates teach as well. (Very helpful.)
Also, the institute sent my resume to ever English speaking institute in town. (Good way to get started.) However, teaching for a language institute has you often times running around town and making as much as nearly half of what you could be making if find your own 1-on-1 students.
I believe there are some internet courses online out of The States that take a weekend and cost US$300-US$400. However, you might have to take some test at a testing center when it's all said and done. Don't know for sure.
Good luck. Being certified gives you license to correct your friends' grammar when you go back home for the holidays. (And they'll LOVE you for it.)