HDB lost $500m

I remember a parliamentary session when it was told that HDB lost $500m in one year or something like that, and the reason was the sale of flats below cost. Someone please correct me if the number of $500m was wrong. What is puzzling to me is that if you are running a business, with the best talents, and you decide on the cost of land, the price you are paying the contractors, and you also decide the price you are selling to the customers, and you lose money, $500m! What shall I say? Must be a lot of subsidies at cost. And who decides what is the cost?