So far, we've been playing around with a SM+0 robot, and extrapolating all the costs for systems much smaller than the creators of spaceships ever intended. This method works, but we can make this simpler, while doing so gain many more options for robot sizes. Many otherwise similar robots will differ mainly in size and gear tacked on at the end. Rather than buying systems at the size the spaceship will be, we will build the spaceship at an easy to calculate abstract size, and then scale it to the size that we need.
While this is being presented as part of the robots as spaceships series, this is a tool I've been using for a long time when building spaceships. It simplifies table look-ups, and gives us a lot of power and flexibility we can use to build spaceships that aren't exactly on the SM benchmarks.