Consensus is an important concept in group decision making. Although various methods have been proposed to derive agreement among experts, the decision cost in the mediation process is scarcely considered. This paper focuses on the decision cost in group decision making and develops a multi‐round mediation model under the constraints of decision costs. After experts provide advices within the analytic hierarchy process (AHP) framework, the proposed model integrates expert advices, estimates the decision cost to reach consensus and updates expert weights to conduct further mediation. This process continues until the consistent opinion is achieved among experts or the decision cost exceeds a maximum threshold. A numerical study shows that the proposed model provides a guideline for the AHP group decision‐making problems to reach acceptable consistency under cost constraints. Copyright © 2012 John Wiley & Sons, Ltd.