Financial news channel CNBC is reporting the airline loses due to the airspace closure are $200 million per day, and air cargo losses (including losses to non-aviation businesses that cannot deliver products) at $100 million per day. $1.5 billion over the 5 days so far.
(which sounds a bit low given the individual daily losses reported by BA, KLM, Emirates, etc., but perhaps those have "ramped up" as the crisis deepened).
In viewing the arguments on either side here, my sense is they boil down to "airspace should be open until it is proved unsafe" vs. "airspace should be closed until it is proved safe."
I'm not sure it will ever be possible to prove either case. 100 successful test flights are no guarantee that the 101st won't glide home with fused engines.