This paper proposes a three-tier process for supporting policy planning of urban agroecosystems. It comprises the following steps: (i) definition of the agro-environmental unit; (ii) measurement of the non-market values; (iii) estimation of opportunity cost. An application to an urban wetland agro-ecosystem within Mexico City is used for illustrating our methodology. We estimated that the wetland agro-ecosystem has a lower-bound monetary value between $15.6million and $31.5million USD/ha/y. As the land conversion rate is about 3.73ha/y, the opportunity cost would be between $22,300 and $44,900USD/ha/y. Such figures are an objective way to appreciate both the potential enhancement value and the opportunity cost of ecosystem services adjacent to urban areas, providing both urban and environmental policy guidance. We argue that this framework allows for multi-scale analysis and may be applied for other urban ecosystems as well.