A few yrs ago I heard a great story on NPR about the minimum spend. I dont think 250$ per day is bad but others may differ.
http://pri.org/stories/2011-05-17/wh...200-day-bhutan
What i like is the comment vs nepal "Some Bhutanese look at what they see as Nepal's pot-smoking, penny-pinching backpackers, and chaotic tourist quarter, and say that's exactly what they don't want. "