So a lot of people seem to agree that battleships/cruisers should have much tougher armor, and very little shields (just enough to protect against annoying little asteroids and pesky NPCs). Not many people agree that battleships should be faction-only. I admit that I was reluctant to suggest that, and I've normally been a big supporter of independents having the same rights as factions.
But increasing the price alone isn't going to dissuade people from buying their battleships. Change the price to a billion credits, plus weapons and armor, and there'll still be tons of them running around, especially if they were changed to be actually useful, rather than just giant targets. Unless trading becomes much less profitable (which it may be from what I hear), there'll still be a fair number of PvP-whores buying the biggest ship they can find.
Making all/most/some/the best battleship weapons use expensive ammo is an interesting idea. Would people be using battleships as much if you not only had to pay over a billion credits to buy/outfit it, but also have to spend a hefty chunk of change to repair it after any real battle, AND have to shell out the cash to buy the ammo for all but your weaker guns?