The Software Engineering community has been trying to get fast and accurate software estimations for many years. Most of the proposed methods require historical information and/or experts’ judgment. Because of that, the current methods are not suitable for novice developers or persons who do not know the company development capability. In order to help overcome such need, this paper proposes a software estimation method named CEBON (Collaborative Estimation Based On Negotiation). The method is applicable to small/medium-size projects (1-6 months). It focuses on supporting estimation of Web information systems in scenarios where historical data is not available. The CEBON method has been used to estimate eight real projects. The obtained results were compared with the real projects execution, which were carried out by novice developers in Chile. The comparison indicates the method is able to deliver quite accurate results. In addition, a survey applied to the involved developers shows they feel comfortable using the estimation method. The article also describes a collaborative software application supporting the CEBON process and a preliminary evaluation of both the estimation method and the supporting tool.