I also did the last 3 nights as you suggested, and did indeed get the 80k per night for the non-premium room.

If you click in to look at the available rooms, you will see when its 80k per night additional room options pop up as available that are not there for the full time. It makes sense, since your first 2 nights are weekend. So the basic rooms are booked for that weekend. Just keep checking back for cancelations!