How is your ranking for your bachelor's degree? I.e. were you an average student or better than that? Converting international grades isn't straight forward and you may be better off than what you wrote here. Your math skills seem better than b and c grades if you are teaching the intro math for your MA.
Besides that, it is tough for me to say. Has your masters sent people to finance or econ phds in the past? Where? How do you compare to them?
My guess is that you should apply widely in the 10-50 ranking. The wide range is because I am uncertain.