Being in construction I could see that figure of a half million. Here are the things to look at (1) I have never been in a hall where land was donated it just doesn't happen today plus the wt. Is picky where to put the building. In large populated areas land is costly. (2) This is a commercial build not a residential build. Codes and permitting is costly. (3) Material cost alot today and being commercial build even more. (4) Even though many give their labor free there is still ones who get paid. I knew many brothers who charged for many items in the construction of KH.
Not to burst your bubble here is another example. I live in a 120 year old farm house. If I lost my house due to a disaster according to my insurance policy the replacement cost would be almost 250,000 dollars. This is just the building not the land.
I am sure the borg is making money on it somehow mostly in resale but it does cost alot today to build a KH today. Still Totally ADD