My group is level 19 and we are currently messing around on an island chain near the coast. Our whole team is into the idea of making an epic-level submarine. Our Wizard, Artificer and me (the Bard) are willing to sacrifice alot of time to help make it work. We also have a long standing favor to call upon with a Dwarven city state that we saved.
We would use this as the basic layout and size but with magic cannon and harpoon cannon instead of torpedo launchers. Between us and the dwarven blacksmiths’ and tinkers’ guides helping us as a favor, How much time and GP it will take going off the handbook?
PS. In our group if we come to the DM with a fully formed idea and alot of the work done already he is more likely to clear it. So he is unaware of this plan so far.