cruisers cant get too cheap, or powers that dont deserve them will get to buy them, like Germany, ANZAC, and Italy. Sure they can buy some, and use the unit, but its expensive now for a reason, so they dont buy a gazzilon.
Boat prices have to be high, because only wealthy powers deserve big fleets.
if you want to add something neat to destroyers add my Sonar/Radar tech to games
“In addition to Radar as normal, a power with this breakthrough is also granted Sonar, Destroyers now fire pre-emptively on the first round of combat at submarines when both attacking and defending.”