Black Vitriol

About 39s 99c on Beta · Horde (8 hours ago) and 1g 55s on Beta · Alliance (10 hours ago), from player scans. A vendor pays 10s 0c, so the auction house pays 3.8× more.

3 recipes: Soul Vessel, Philosopher's Stone, and Alchemists' Stone.

No. It is in Classic Era too, with the same item level, vendor price and stack size.

Sell it on the auction house. After the 5% cut a stack of 20 brings about 7g 59s there, against 2g 0s at a vendor.