$300.

As others have said -- supply and demand is the biggie.

Now if you are in a hotel where the standard double room is $300, $600 will get you a much nicer room, usually a suite of some sort. Size, location and amenities are all available for a price. Question is do you need the nicer room or do you have higher priorities for the money. I'd rather do a show and/or special dinner.

Sometimes I'll pay extra for a club floor room ($20 to $80) as I will save the cost of breakfast and enjoy an afternoon snack. Overseas mostly you can sometimes have a free drink as well. I never pay more for a suite as I spend so little time in the room I have no use for the extra space.