You can't predict stock price because that will depend on the # of shares issued - and the valuation. If they issue only one share and the company is valued at $80 billion, that share will be $80 billion dollars. If they issue 80 billion shares, the price of one share will be one $1 dollar.
But what you can try to speculate on is the valuation of the company.
$80 billion seems like a crazy #______Ford is currently valued at $65 billion.
So Rivian is asking to go public at a company net worth that is greater than Ford Motor Company.
I think, and hope, Rivian will do great. But they are not going to be making 3 million vehicles a year anytime soon. In fact, I think the predictions of when they will get to the point of producing 500,000 vehicles in one year is off in the distant future.
Something to remember, a good company can have a stock that doesn't perform that well.