I currently have a 100 gal propane tank owned by the propane company.
It is refilled by automatic delivery and the price is set by the company.
At one time I had a tank owned by another propane supplier.
I switched from that company to the company I currently use. This
required that the old company had to come and remove their tank. I was
reimbursed for the propane left in the old tank. The new company
installed their tank and I was locked into whatever price they charged.
I want to own my own tank so I can shop around for the best price when
having my tank refilled, much like I do with my fuel oil tank.
Having googled for 100 gal propane tanks, it seems that no one sells
these large tanks to the general public. Even eBay does not have any new
or used tanks for sale (Your search returned 0 items).
Anyone have any ideas?

You must ask in your own location, Grasshoppah. Some states may have
statutes that eliminate private ownership. Liability is a big issue, even
if you have everything right, and have the tank inspected, yada yada. I can
buy one in my state, Utah, but I would have to live a very long time for it
to be a deal. Plus, as the nice propane lady told me, if I have any problem
with the tank, they just bring me another one, no charge, no repair. I
don't believe that would be the case with a privately owned tank.

If your issue is finding the cheapest propane, and the costs vary enough to
make it mathematically justifiable, they by all means, shop around. First,
though, ask the basic questions where YOU live, as some of the answers here
will be worth the paper they are written on, as they won't be valid where
YOU live.

Some suppliers, particularly of propane have been known to have wildly
fluctuating prices, taking advantage of some people they have captive by a
lease, etc.

Good luck.

Steve