There are many different ways to build your own house, your own car, your own boat, your own RV and even your own airplane. But what about your own submarine? The ocean realm, after all, makes up a majority of the planet's surface. It turns out that personal, DIY submarines are being built.
Sometimes they are not very pretty, as seen here:
Although it is not pretty, the beauty of the design is that you can see what he is doing. Thick acrylic creates windows. The motors and propellers are obvious in what they do. The shape is not elegant, but would make for easy welding.
This video indicates that a large propane tank could be used as a starting point:
One of the most sophisticated DIY subs is called the Nautilus, seen here (be sure to turn on closed-captioning):
A tour of the Nautilus hull:
Diving in the Nautilus:
If you try building your own submarine, you will not be alone:
If you take off the requirement for full submersion, then you have a DIY drug sub like this one:
If you would rather buy than build, here is an option that doesn't cost much more than a car:
Details on building your own sub: