The problem with DDG1000/Zumwalt's ammo is that the guns aren't just regular 155 - ie you can NOT put regular 155 army arty rounds in them. The current rounds are 88 inches long, and the auto loading and storage system is set up for just these rounds. These rounds do have different variants, some rocket assisted, some not, but they are all specialized rounds which have no compatibility with land based 155 tubes ammo.
Each of the 3 DDG1000s can hold 600 rounds ready to go (300 per turret), and an extra 150 rounds in storage. At current prices, to fill up each ship just ONCE with gun ammo, the cost is higher than buying 2 full squadrons of Super Hornets (24 aircraft) for the Navy.
Also, the Zumwalt has been super neutered. No SPY1/Aegis system, just a dinky mid ranged air defense radar and only ESSM SAM missiles. No Standard missiles, no SeaRam, and NO Ciws system of any kind. Dumb. Also, only 80 VLS tubes, less than a Burke destroyer. They've also compromised on the stealth with so many design issues that it's ridiculous. It does have some good new features, it's a tough ship, and using VLS tubes as "armor" as well was a smart idea the way they did it, but the ship is very under armed, and has too few long range sensors as well. Now, the only ace on the table, the guns, are neutered too, and even if they DO build some cheaper ammo, that'll mean that the big advantage, being able to bombard land or sea based targets from a distance so far that it's hard for them to hit back, is gone, as regular ammo = being as close as normal ships are when using guns vs land based targets. Thus, putting the DDG1000s right back into harms way as they are visible with optical tracking at those ranges, and stealth won't mean crap there.
What they should do now IMO is if they can't solve the ammo/price issue, is on the next 2 ships remove those guns, put a single advanced regular gun 5" class or whatever, and use all that extra space to stuff in 100 or more VLS tubes, giving the ship nearly 200 VLS weapon tubes. Also put a SeaRam in some sort of stealth mount or a retracting mount there too.
I hear the OP on the state of the air combat forces, posted before about this too, right now over 1/2 of the USMC fighters aren't able to fly much less fight. Situation is intolerable right now, hopefully things will improve starting Jan 2017.