Cosmic rune

Cosmic Rune is a free-to-play item on the OSRS Grand Exchange in the runes category.

In-game examine text: "Used for enchant spells."

It has a Grand Exchange buy limit of 18,000 every four hours, a high alchemy value of 30 gp, and item ID 564.

View on OSRS Wiki

Cosmic Rune shows an active flip setup with a margin of +3 gp and 10,045,767 trades over the last 24 hours.

At the buy limit of 18,000 every four hours, max profit per cycle is about 54.0k gp — high margin with healthy liquidity.