Recent studies that incorporate the spatial distributions of biological benefits and economic costs in conservation planning have shown that limited budgets can achieve substantially larger biological gains than when planning ignores costs. Despite concern from donors about the effectiveness of conservation interventions, these increases in efficiency from incorporating costs into planning have not yet been widely recognized. Here, we focus on what these costs are, why they are important to consider, how they can be quantified and the benefits of their inclusion in priority setting. The most recent work in the field has examined the degree to which dynamics and threat affect the outcomes of conservation planning. We assess how costs fit into this new framework and consider prospects for integrating them into conservation planning.