Since the RFP for phase one included the underground to Eau Claire already, it is going to face major scope changes. So, I say they accept the UCP alignment and then start re-design. Send back a crayon drawing to secure funding grants and build it to the Event Centre. You can deal with any cost changes, or adjustments in the future. Just get that money in the bank and start.
They want to discuss risks, and how these will probably make it cost as much as the underground, which I agree with, but don't forget the risks the underground would have seen raising the costs 1-2 billion more than they said it would.