3 to 5 times annual revenue is indeed typical. From there on it's all handwaving about "exponential growth" and "strategic value" to get more than that.

You are "worth" what they are willing to pay, it's that simple. In terms of money, you're worth about a million dollars. But it wouldn't be that weird to get much more, depending on how good you are at handwaving about "strategic value" and "exponential growth", and playing the negotiation game.