Try GritEcon.
http://imagemodserver.mine.nu/other/MM/SE4/Mods/
In that mod, ship build times go up proportional to size CUBED.
Maintenance costs are flat rate.
So it costs about the same amount of resources to maintain two 200kt scouts as it does to maintain two 800kt battleships.
However, those battleships take 64 times longer to build.
Thusly, big ships are super-awesome, but really hard to acquire. Small ships are nessesary as cannon-fodder in combat to protect your larger ships.