My usual advice would be to go ask one of your professors what he/she thinks your chances are. If your public policy professor is actually an economist and has written letters for lots of students for PhD programs in Economics, then you can ask him/her. Letters are really important for admissions (from what I've gathered), and it seems like letters from non-econ/math people are weighted much less heavily (than letters from econ/math people). If you are applying this year, you may have a tough time in the 20-40 range given that the only math you have during application is Calc 1-3 (and LA and Numerical Analysis at schools that let you send fall grades) and your grade in Calc 3, the most advanced of the sequence, is a B+.
Then again, I'm a lowly recent graduate (from undergrad.) so its best to speak with a professor (or grad. student).