what is this leaguestone worth?

I only see 1 additional essence leaguestones on poe.trade, price estimate?

It's an Essence leaguestone, nothing special I'm afraid. Yeah, it's stacked with Essence, but you can just keep slotting normal ones in for virtually no cost.

If you're not sure about price, list it for 30 chaos and drop the price every day till you sell it.