I do not mean to scare you, but in your case, 100 ( if you have it) % average in undergrad coursework means very little. To compensate you need two things, 1) Strong letters of recommendation, preferably from people who hold phds - if you've had this in mind for the past 3 years, you probably have good relations with some of your professors, 2). Take the GRE and ace it, it could help compensate your signaless degree.
1) + 2) Could help you get into some master degree abroad and get a decent job afterwards.
Easier said than done. If your are talking about the top 3 masters programs in Mexico, you'll have an easier time studying abroad. Unless we are talking about top master (theoretical) degrees elsewhere, then you'll have comparable suffering.
Seems to me that a master in econ, at this moment, is not for you. You should be looking at those business + econ, applied + econ , public policy master degrees or simply work for a year or two and see what you think.
By the way, if you want to get into a top MBA, you probably need at least two years of work experience at some middle management position + sh*t load of money.