I'm thinking about a new career in amateur sub-building. Here's 34-year-old Tao Xinglai showing that anyone can do it, really. All it takes is a little ingenuity and scrap metal:
Total budget? $4,400. Of course, if we wanted to take it up a notch, there's Peter Madsen, who built the largest homemade sub in the world, the UC3 Nautilus:
Total cost: "millions of Danish crowns"—though it was still cheaper than a professionally built diesel submarine. But it might be easier to build your own submarine in Denmark, where anyone can build their own vessel without permission, as long as it's shorter than 24 meters. Meanwhile, the state of New York seems to look less favorably on makeshift subs gurgling along the channel.