Protected areas are the primary management tool for conserving ecosystems, yet their intended outcomes may often be compromised by poaching. Poaching can be prevented through educating community members so they support protected areas and enforcement, but both activities can be costly. Consequently, many protected areas are ineffective ‘paper parks’ that contribute little towards conserving ecosystems. We develop a model of enforcement in a marine protected area and ask how much does it cost to enforce a marine protected area so that it has greater biomass of fished species than a paper park or has fish biomasses that meet ecological targets. Using a case-study from one of the most biodiverse reef systems globally, Raja Ampat in Indonesia, we find that slight improvements in the biomass of fished species beyond paper park status are relatively cheap, but achieving pristine fish biomass is far beyond the budget of most conservation agencies. We find that community engagement activities that reduce poaching rates can greatly reduce the cost of enforcement. Thus we provide dollar values that can be used to compare the value of community engagement with the cost enforcement. We conclude that the current policy of protected area enforcement is an ineffective way to manage protected areas. Budgets for park management should be optimised across spending on enforcement and alternative activities, like education to build community support. Optimized budgets will be much more likely to achieve ecological targets for recovering fish biomasses.