In my version the oil tanker is the only new unit added. Well, apart from Radar installations and Rocket pieces.
But then one key rule I introduce is that all ships must refuel every turn, tying them to friendly land areas. With tankers it becomes possible to carry out long range naval operations, but the pieces themselves are expensive and have no combat value.
I’m not convinced that cruisers are anything more than a piece for the sake of having a 3-3 ship, with destroyers becoming 2-2, but we’ll see what LH has come up with in Guadalcanal. Eventually.
The problem with cost reduction is that you might create naval cannon fodder units bought in vast quantaties just to soak up hits. A ship costing 4 IPCs and having no combat value would probably be a good buy.