What is the difference between Cheap and Expensive Perfume?

The primary difference is in the construction of the perfume. a cheap perfume will have a few more readily available notes. A more expensive one will have base, middle and top notes and using rarer and more expensive ingredients, but of course the primary difference is the price. Brand names trade on the exclusivity of the brand. So whilst the cost of the ingredients may result in a base cost of a premium brand being double that of a cheaper perfume, that still only represent single digit percentages of the high street price. The rest is down to marketing and margin, brands spend more on marketing and have a higher margin.