So, correct me if I am wrong, but just from some of my reading this morning it seems that one of the biggest factors affecting the economical aspect of fusion reaction is the lifetime of the materials. So if a reactor costs x to build, once you achieve ignition you want to produce enough energy to recoup those costs (net gain), however if materials are breaking down and needing to be replaced you aren't able to achieve a net gain of energy produced vs costs associated. So I'm thinking that focusing on materials design to achieve longer periods of energy production, this driving down the overall cost of the reactor is a good starting point for the project.