Best Mine for around 7,500,000 Cr

[Jeb T. Firefly]

Hey! I just managed to scrape together this amount of credits to buy myself a second mine...
I'm at around 130 sectors to 0,0. Every single thread on this is at least a few years old, so I figured I might as well start a new one.
Fleet assets are:
2x Mining Ships (One using regular lasers and the other R-mining lasers)
2x Combat Ships (Both with a few Exotic weapons)
1x Shipping Vessel (Bunch of cargo space)
1x Oil Rig asteroid mine

With these assets, I'm looking to add another mine to my Empire. With 7,500,000 in the bank, I can afford most of the Noble Metal Mines, another Oil Rig, a Coal Mine, or an Ice Mine. If there's a REALLY good mine just out of my price range, I could grind another million or two.
What mine would be the best in terms of single-unit profit (i.e. not part of a production chain)?

[Johnson1893]

Use the orange/red trade scanner, see the statistics of goods in the nearest sectors. You are interested in any noble metal with the maximum demand and minimum supply in the nearest systems.
There is no panacea, any production needs must first be investigated.

[Jeb T. Firefly]

The best trade scanner I have only shows what goods I can sell and buy plus the price deviations (Electron Accelerators for -23% the base price)...
I don't have a huge number of trading upgrades, but I have found a research station. Should I just buy a ton of bad Trading Systems and then stack them all together for a better one?

Oh, and I found an asteroid with a Trade Outpost that buys gold, so I made a Gold and Platinum mine with a few cargo shuttles that's made me around $10,000,000 in the first hour or so of operation, so I get what you're talking about. One thing I'm unclear on, though - do stations only request goods from bits of supply chains in their sector, or do they request goods from adjacent sectors as well?