[Puke]

still think a series of hull size classes should dictate the relative building costs (scaled by your construction/materials technology level) according to how big the final design really is

Wow, I really like this one. This idea should be 'bumped' by more people.

basically, you dont have to choose your hull size, but the cost of building larger things might exponentially increase as size goes up. increased levels of ship construction would afford you a more generous formula for cost / mass ratio.

furthermore, speed of a ship is calculated dynamically by thrust vs mass. engine technology provides greater thrust, and ships can be ANY mass.