November 18, 2012: Over the last two decades, luxury boat builders have begun building recreational submarines in large quantities. There are now hundreds of them in use, some built by hobbyists...Wired has an article about it HERE.
At the low end you have hobbyist home-builts that cost less than $50,000 for components, plus over a thousand hours of labor by the do-it-yourself submarine builders. Commercial subs starts at a $100,000
You can buy a kit here for $50 thousand dollars.