Maybe look at a good MS or MA in Economics and go from there? Most do not have the math requirements that PhD programs do. You might look at terminal masters at schools without PhD programs (you'll get more faculty attention). U Colorado - Denver, Montana State (good in natural resource), Baylor, and SUNY are good ones that I'm aware of. You'll be able to shore up your math while there. You'd also have research experience going into a PhD, which could potentially shorten your time to completion (if it shortens your PhD by one year, your opportunity cost is roughly one year).