The paper examines the trade-off between cost and performance of a hypercube based computer interconnection network founded on a detailed cost analysis model. A cost function is proposed which considers the economies of scale of bandwidth available through optical fibre communication and the nonincremental increase in node complexity resulting from variations in network size. When considering topology choice, an important consideration is expansion. Any comparison of expansion should be done through marginal analysis: weighing the additional benefits (performance) against the additional cost resulting from expansion. To demonstrate this technique, four interconnection networks are considered: booleann-cube, nearest neighbour mesh hypercube, generalised hypercube, and spanning multiaccess channel hypercube. Systems with equalised performance are studied, investigating the variations in cost. This permits the investigation of the trade-off of performance/cost between high capacity communication channels and increased number of channels and degree.