You are confusing Trump's properties. Doral is not the resort Trump typically stays at, it is not on the water but inland. It would appear you are thinking of Mar-A-Lago. I don't believe that Doral is a property that the Secret Service has permanently secured, in fact, I can't recall Trump staying at Doral as President.
Next, what is "cost?" "Cost"is one of those words that can often mean what a business owner wants it to mean -- such as when people buy a car at "dealer cost," the dealer is typically still making several hundred (or a couple of thousand) dollars of profit, based on a whatever "kick backs" the manufacturer gives them for selling cars.
More to the point, Doral has been struggling and, as pointed out, August is low season for the resort (very few bookings). As such, just bringing in the G7 makes Trump money as, even if he did sell them all for cost, these are rooms that are now paying for themselves rather than sitting empty.
It is also unclear who this was going to be "at cost" for -- it appears he largely intended that it only to be at cost for the US government. That is the big issue, the fact that Trump stood to directly make money off of foreign governments -- with per the emoluments clause, is against
the Constitution for a sitting president to do.
