Because the letter "h" is not a vowel sound. But there are exemptions to the rule. If it is pronounced in vowel sound like for an example, "hour", an is should be used.
"The cost of a two night hotel room at Cyclades Hotel may vary. For a single person, the cost may be around one hundred and fifty to three hundred and sixty dollars."
Construction costs would depend on size, location and facilities included.
Rental cost for a room would depend on size, location and facilities provided.