Softbank is apparently ready to spend $10 billion on the deal, but the auction process it's after may value Uber at around $50 billion. Uber's current valuation is about $68 billion, so—although some investors may be keen to cash out after a tumultuous year—the company would have some convincing to do.
Valuation just dropped because of that, Softbank is winning already
http://fortune.com/2017/09/15/softbank-uber-discount-investment-valuation/