The battleships cost what they do for a number of reasons.
1. They're resin, which is always going to be much more expensive than mass-produced plastic.
2. They have no chance of selling in the kind of large numbers the plastics do, which makes it even harder to keep production costs down. They cost too many points, eat up extremely rare slots in the fleet org table (you can't even put one on the table in small games), and are generally kind of iffy in effectiveness compared to equal points in cruisers & frigates - although the recent rules tweaks helped with that some, especially for the New York class and as a base for your admiral (who also became more important when the command cards arrived).
3. And lastly, they're all packed with the parts to make all their variants, and most of them can easily be magnetized or pinned to let you swap parts around and field different classes as desired. That not only eats into sales even more, it makes them more of a bargain than they appear, especially the UCM ones (which are the easiest to do parts swaps with and have three variant classes, not two).
They do cost a lot, but you don't really need them to play and no one is ever going to need more than two (and even one is plenty for most) for any normal game.