The increased use of advanced composites in aerospace manufacturing has led to the development of new production processes and technology. The implementation of advanced composites manufacturing technology is poorly served by traditional cost accounting methods, which distort costs by using inappropriate volume-based allocations of overhead. Activity-based costing has emerged as a methodology which provides more accurate allocation of costs to products or activities by their usage of company resources. Better designs may also be produced if designers could evaluate the cost implications of their choices early in the design process. This research describes a methodology whereby companies can improve product cost estimation at the conceptual design phase, using intelligent searching and arrangement of existing accounting data to enable designers to access the activity cost information more readily. The concept has considerable scope for application in industry because it will allow companies to make better use of information that is already being recorded in their information systems, by providing it in a form which will enable designers to make better informed decisions during the design process. The design decision support framework is illustrated by applying it to a typical problem in aerospace composites manufacturing. Feasibility of the approach is demonstrated using a prototype software model of the Design Decision Support System, implemented using commercially available software.