If the Eli Lilly commentary is right and they can produce 1m of their single antibody monoclonal by year end, and ramp up production of their cocktail mix to similar levels early next year then we're looking at a massive leap in capacity. Who else could do the same (if they had guaranteed sales even if their product wasn't used) I don't know, I do suspect the cost may be a drop in the ocean compared to the broader economic costs (never mind the human ones). I don't think it's unreasonable to think that the cost will rapidly drop below £1000/patient and could hit £100 at volume once we know which product we want. Though boring things like patents and copyright will doubtless intervene when it comes to price.
Using it on all 70+ patients with symptoms might have the biggest impact. But in reality that's still one for some mix of clinical trials, statistics, and cost/benefit analysis to prove. I'm hopeful though - I think in the first half of next year, we'll have antibodies for stopping the virus early, vaccines for reducing the numbers of infections and some more treatments for the ones who become seriously ill. Oddly, despite the absolutely miserable numbers of new cases etc, I'm having one of my more optimistic days today.