A simple model describing the scaling laws of tokamak fusion reactors is used to derive the dependence of capital cost on the basic parameters involved. The beta value required for each set of parameters is normalized to an equivalent beta in JET to provide a uniform measure of feasibility. The capital cost is related to the engineered volume per unit of power. The simplicity of the model and the uncertainty of the assumptions exclude a precise evaluation, but do allow an overview of the essential features arising in a reactor assessment.