I might be remembering wrong but i think the Italian rebuilds cost half as much compared to a new one.It's really not. IIRC (and I'm going off memory here so I may be wrong) the American rebuilds of the Standards cost about the same as the cost to build a whole new ship. Maybe a little less, but I'm talking like, 5 rebuilds for the price for 4 new ships
In case of the Germans any cost can be rationalized because you're not allowed to buy a new one, though where a rebuild ends and a new ship starts is an open question.