[Fyron]

You need to have the retrofit add cost at least 100%, if not higher, for retroseries builds where you are just adding new components. Having a negative cost for removing a component makes normal upgrades cheaper than gamey retroseries builds. You can even do something fun like 200% cost to add a component, -115% cost to remove it. Note that you can never gain any resources from a retrofit. This makes adding components in a retroseries 2x as expensive, while upgrading a component to the next version in the family is a bit less expensive than the cost of the component alone. It also makes it so that if you replace your DUCs with APBs, you pay a lot more than just upgrading DUC I to DUC II, but still less than if you were just adding APBs to an empty hull.