At first I was thinking US$9000 WTF??? But actually, if you think about it, a 20m2 room at the Alvear, Duhau, 4 Seasons, Hilton, etc can easily cost US$300 (or more!) a night.
So, if you are 4 people you'd need two rooms, 6 would need 3 rooms. Frankly, if I were visiting for a month with some...