Yet again, the humble Type XXIII gets short shrift.
I'd certainly own a Type XXIII. Small enough to be manageable with a small crew.
Besides, it's vaguely possible to build one if you have enough cash:
This is the UC-3, being built by Peter Madsen. It's about 10 meters shorter than a XXIII, at ~25 meters instead of 34 meters. It does show, however, that you can do something roughly on the same order of magnitude.
His previous boat is for sale, by the way. It's called the "Kraka", and is roughly 1/2 the size of this one. It should look vaguely familiar:
It's a steal for $248,000:
http://www.psubs.org/forsale/