You are not charged for the service cost of the ships (which is high), but you are still charged the ammo cost just like everyone else!
You don't HAVE to do any of that.
Try to keep a little perspective here, please. This is an opportunity to test out the super ships before Ranked begins. For coop, you do not HAVE to put any modules whatsoever onto these super ships. You do, however, HAVE to pay the meager ammunition cost to play it. If you choose to put modules onto your rental superships (like any other rental ship), then you will keep them when the rental period expires - they just go into your inventory and wait for assignment to a new ship.
Sorry, but I don't have much sympathy for the "WOW WG" about stuff like this.
You don't want to pay the ammunition cost to try new content early? Don't play it.