One of the basic premises of sustainable design is resource efficiency. Meeting the goal of using less material inherently tends to reduce the materials cost of a project.
Materials costs are only a portion of project costs, however.
To help prevent this problem, look for building industry professionals with experience or certification in sustainable design and construction. Most importantly, remember that the key to sustainable construction is holistic design. Taking a comprehensive approach to design will reveal opportunities for savings that otherwise might have been missed. For example, if a home is designed and constructed to have very low air infiltration, and very good insulation, a smaller, less expensive heating system might be used. Similarly, water-efficient fixtures might justify a smaller water heater, or natural ventilation could allow the omission of air conditioning.