Against a background of high-speed development and the expansion of built land surface, there has been widespread encroachment of natural habitats (henceforth “eco-spaces”). It becomes correspondingly difficult to improve the value of urban ecosystem services, since current assessments of land still primarily focus on use value (e.g., when nature and its products are converted and consumed), while the regulation and non-material services provided by eco-spaces are often ignored. In order to assess the rate of return on land transfers of eco-space, theories such as strong sustainable development, ecological land rental, natural resource ownership and opportunity costs were synthesized to construct an eco-space transfer cost–benefit analysis model, which is based on the value of ecosystem services. This study used the Futian Mangrove Ecological Park in the megacity of Shenzhen as a case study. To estimate the social value, which more comprehensively captures ecosystem services and economic value from eco-space, we used a counterfactual scenario of residential land development (the most plausible alternative land use scenario). This allowed us to calculate the rate of return from eco-space use change. The result of the total and annual rates of return over a projected 70-year timeframe were −10.76% and −0.16%, respectively. Accordingly, we suggest that management of the mangrove park should change the pricing strategy to better align the social benefits that it generates with the payments sustaining it. This case study provides instructive lessons for the management of eco-space in large urban settings.