Considering a Planet Ocean..Need a little direction

[looking to buy]

Hello, to date I have been just a Rolex and old pocket watch kind of guy. But, the Orange Planet Ocean really has my attention. The problem is I cannot figure out what is what. It seems there are two sizes. 42mm and 45.5mm. Then it seems like there is a new in house 8500 movement as opposed to an older 2500 or 2900(?) movement that may be an ETA. When I look on eBay, some of them have many bids and some no bids. On this forum the Planet Oceans seem to sell right away. I called a dealer some 75 miles from where I live and he said he has a new 8500 42mm for $4500. I probably have no interest in a new one. Especially at that price.

So I seem to have done as much research as I can but still really have no clear idea as to what is out there and what I would be buying. Any enlightenment that some of you could give me on what seems a myriad of choices would be welcome.