You know, if boats are as expensive to buy and maintain as I've heard they are, chucking a couple shotguns and a few boxes of ammon into the ocean is pretty small change in comparison to the overall cost of such a hobby.
Under power of motor, especialy big motors yes. It costs a lot of money to power many motor yachts. However sailboats under power of sail with motors only as an alternate source can be quite inexpensive in comparison.
I have known several families choosing to live on such vessels rather than in a home, and the cost is close to that of an apartment. In fact I have taken trips with such people on such vessels helping to pay for expenses. It costs little more than going camping nowadays. The main limiting factor is the availability of slips. On most of the west coast there is close to a three year waiting period for many slip sizes.
The dock fee combined with the monthly payments are close to what people pay to rent an apartment, nevermind the mortgage on a home. If you can pay a mortgage on a home you could definately live on a boat.
I have seen adults fresh out of college do it.
So it is by no means out of the reach of the average individual, or even the below average individual. In fact with many people purchasing expensive vehicles every few years, if they simply kept the same vehicle for awhile or got something cheaper than a couple expensive SUVs, pickups, or luxury cars to commute with they could afford the initial purchase of many lower end seaworthy vessels. So it really is a priority thing. You can get a used seaworthy vessel for the price of two new cars, and you could finance it about the same.
Many people also have RVs or a motorhome, if they can afford that they could have got a sailboat for about the same (+ the monthly slip fee.)
It is however an unsuitable lifestyle for many, as it requires being extremely neat, organized and space effecient. It would be like living in a motorhome or RV, but with your life even more dependent on it. If you misplace your emergency gear and are going down, well that might be a death sentence.
If someone can dive and is a decent handyman they can also do most of the maintainance themselves. Most such maintainence is prevention based.
So unless throwing away a gun is nothing to you, or even throwing away the value of half a gun is nothing to you, I wouldn't assume it is for anyone else either. Most of the people I have taken trips with couldn't afford to throw away such money.
I also don't see how that really is related to being armed at sea. If the local authorities are about to board you and you toss an illegal firearm overboard they are going to see it and arrest you anyways. In most nations it is guilty unless you can prove yourself innocent. That means by being charged you have already lost half the legal fight.
If you are planning to throw them overboard before entering the waters of a nation, well then you won't be armed once you leave them, or while anchored or docked in a harbor (where a lot of piracy happens, like in the ops story.