Darkspliver is really close. I am in construction in the USA in the Midwest. Generally, you are looking at $300-$500 a square foot depending on the size, height, type of structure, specialty systems, and grade of interior finishes. A simple office building complex with residential suites would be about $400 a square foot. However, the $400 a square foot includes union labor. As we know, the real estate company, WTBT$, was built on free labor. Since many of the labor manhours are donated, the org gets a break. It can be said that about 50% of the cost, is labor. There still is cost involved with free labor such as housing, food, and other expenses. I would probably figure a 35-40% discount due to the free labor because I believe that they do subcontract some specialized work. Also, my personal experience on quick builds (do you remember those?) demonstrated a lack of serious rates of production as well as work that had to be done over again with additional material costs. I estimate about $450,000,000.