Starship AI Valves have a base price of 12 million units each. I don't think you can dig these up, though. The only way I've ever gotten my hands on one is as part of the loot you get for scrapping a starship, and I think they can be gifted to you very rarely by NPCs.
The Fusion Igniter and Stasis Device are currently tied for the commodity with the highest trade value in the game, with a base price of 15.6 million units each. You can craft both of these but they take a large amount of specific materials and multiple crafting steps to generate from the whole cloth, and require knowledge of several advanced blueprints, all of which makes it a pain in the ass. Despite their high resale value it's faster and easier to employ other ways of making cash.