Surely a Craig B solo gig with more than 70 people would lead to greater optimism than that! Anyway, as the man said, let's stop Hi-jacking The Twilight Sad thread.
I think it's an Lemon Tree (APA) promotion and yes it isn't exactly cheap but it holds 550 people so that comes into play. I'm sure (well partly guessing) that there wouldn't be disimilar costs if you wanted to hire The Warehouse.
Years ago I did some work preparing budget costs for a scheme which I can't remember the details of but even then the cost of draining/keeping dry was prohibitive.
That is what you should do! Depending on how far ahead you're booking it is worth checking Travelodge for cheaper deals although typically these seem to be less available in Aberdeen than elsewhere. But sometimes, especially weekends.