Your work experience is great, I think you can apply to the biggies. Was your GPA low because of a particular class or particular classes? From what I know, more than your overall GPA, they look at specific scores. For example if you aced your IR class but did badly in say, linguistics, you're fine. In the optional essays, you can explain that the reason you did poorly in X subject is because of Y reason. However, if your grades in politics/econ classes is low- then maybe taking up some community college courses or a diploma programme and acing them will offset our scores. That's just my opinion.
I think Kaneisha, who frequents these forums, is exceptionally good at transforming challenging cases. You can try contacting her. Her website is artofapplying.com. I find her blog posts useful as well.