What makes one XO brandy/cognac more expensive than another?

A lot of the reason the big 3 Cognac have very expensive bottling's (ie: above $100) is simply the hype around there brands. While most of the stuff released by Remy Martin, Martell, and Hennessey is pretty good there are other small brand cognacs that are far better. Give this one a go, its called Paul Giraud Elegance Cognac. Its actually the "budget" level bottle in Paul Girauds range but it is still far and away better then anything made by the big 3, even there $1000+ bottles.