In South America the standard minimum requirements are a BA plus a TESL/TEFL Cert. and/or experience.
Of course, as with any job, the more you have to offer in terms of qualifications and experience, the better your chances of landing a well paid job with opportunities for advancement.
Unless your intention is to remain within the ESL industry and build a career for yourself in this field then you could opt for a TESL or TEFL Certificate. This will allow you to get a taster of the ELT profession and see if it is really for you before committing your time, effort and finances to get to the next level.
Being certified will make you more marketable and it will also, and perhaps more importantly, prepare for the job.
Online courses are a good option particularly if you have a limited budget to further your studies or if you have other work and/or family commitments that restrict the amount of time you have available to study. See the ICAL
www.icalweb.com for quality online courses and a respected TESL/TEFL Certificate.