Good questions. I'm only just getting into MD, but I've been a collector
of many things for decades. And I don't mean eBay collecting. When I was a beachbum in Florida, from 1992 through 1993, I survived strictly by beachcombing, without detectors or magnets or scoops, and I sold anything that I couldn't wear, drink or eat. Starvation will set your priorities straight
real quickly when it comes to sentimental treasures.
But, once I settled into a comfortable routine --- that is, when I was feeding myself regularly and had a little luxury time on my hands --- I started a couple of money-making enterprises right off the beach. One venture was swimming out a couple hundred yards or so and free-diving to retrieve these great big, live sand dollars. They averaged about 6 or 7 inches in diameter, some up to about an inch thick, and I'd just fill my pockets with the things, then return to shore and spread them out on a beach towel, where the throngs of tourists could see them. Invariably, this drew a crowd and, invariably, they would offer me money for the sand dollars (bleached, dried out and sealed, these things sell for, like, $3 apiece at souvenir shops). Some folks wanted me to swim out and retrieve giant sand dollars
especially for them, which was no problem,
and it was entertainment. On my best days, I could sell around 70 of those sand dollars at $5 a pop.
The other venture was a little more demanding. While fossilized shark teeth, and even perfectly beautiful fossilized shark teeth, are abundant on Florida beaches, there
are things you can do to enhance their monetary value. Such as buying a spool of cheap gold wire, wrapping the horns of the shark teeth with the wire, and twisting it into a loop to make --
ta daaaa -- shark teeth pendants. A spool of gold wire could wrap about 50 or 60 prize shark teeth, and that's how I spent many a pleasant afternoon in the shade of a palm tree on Siesta Key. Then, on the weekend, I'd catch a ride to any of several flea markets in the area and sell off the pendants. Depending on the color, size, luster and species of the shark teeth (which are easier to find than pulltabs when you know where to look), you could ask anywhere from $1 to $10 and more
per tooth... The big Megalodon teeth can bring
real money, but they are usually found at open-pit mines far inland, and rarely at the beach (I only found fragments of Megalodon, which are basically worthless). In one summer I hunted up over 3,000
perfect specimens of fossilized shark teeth, and sold the majority of them.
To me, this was
real treasure-hunting, taking the treasures of Nature --- which are
right there at your feet --- and turning it into currency. It saved my life, quite literally, and it was an experience that I would never trade. Although, if I had it all to do over again, I think I'd try a metal detector first.
....versus the fact that I end up with some rusty iron and pull tabs gets me every time. Of course ,if I ever hit the big one....my story might change. 
