Over the next few weeks I am temporarily handing my campaign off to a friend to run an adventure arc that takes place almost exclusively underwater. I have considered various methods of solving the issue of water-breathing for the PC's that need to breath, but we both agree that a clockwork device fits best into the theme of the campaign since clockwork items have been used in so many other areas and encounters. I would like some help with constructing the item, determining cost, limitations, etc.
I'm also open to considering other underwater items or whole sets of diving gear if someone has the time to put the work into it.