[Suicide Junkie]

50% of the total cost, minerals+organics+rads.
Make your first build cost even amounts of each resource, and then retrofit to your mineral-heavy regular ship designs.

Retrofits remove all the old components that are not in the current design. The new components will start out damaged.
Changing the order of a component will not cause it to be "reinstalled", it will move for free.

Figure out the total number of components per turn you will need to repair when your factories are running at full speed, and build what you need.
One or two is probably good. If you have a stack of 4 or 5 construction bases that are all pumping out retroseries designs, you may need more.