Here, I tweaked some of my ships to meet the cost and mass requirements. They unfortunately can't compete because they use modded materials and limit editing (encapsulated fuels and complex geometry armatures).
After spending an evening working on cost, I was surprised to find I could take a 17 Mc design down to 5 Mc without loosing efficacy. So I am changing my vote to 5 Mc. It just takes time, especially when starting from the context of the stock designs.
I will say that as my gunboat has evolved, the safety factor all around has become so low it would practically be a war crime to make people crew these ships.
I also like the idea of dedicated tournaments to explore specific combinations of doctrines. Just not for this first round. Maybe for the next, with a 2 Mc limit?