Deliberation may increase the quality of decisions but also necessarily takes time and effort and hence will have costs. But proponents of deliberative democracy as an attractive or superior method for making decisions almost all focus on presumed benefits while in practice ignoring the costs associated with investing time and resources in the process of deliberation. We show that the cost side significantly influences the performance of the deliberative process. Through a number of simulations, we demonstrate that there must be a certain point beyond which the costs of deliberating will outweigh the potential benefits. Since this type of processes invariably will be time consuming, especially when the convergence of the participants towards a common goal is slow, conditions are derived where the deliberative process performs relatively well or relatively poorly, both as concerns the probability of reaching an agreement and in the net benefits to the participants. This is especially the case when the number of participants increase.