What percentage of the 250 ships were warships? I would say that the more warships the better.
If you are worried about the cost of the AI vehicles, try this idea in the AI design creation files. Design the non-warships and bases as small as possible. An example of this in the default game would be to make the Base Space Yard only 500kt at all time.
Name := Base Space Yard
Design Type := Base Space Yard
Vehicle Type := Base
Default Strategy := Don't Get Hurt
Size Minimum Tonnage := 10
Size Maximum Tonnage := 500