The Dragon Lore is nowhere near the most expensive skin in CS:GO- sure, it's worth around $2000 which is a lot, but it's not the most expensive skin. Neither is that knife, because that's a one-off sale and is not representative of its usual value for knives like it. In actuality, no skin is the 'most expensive' skin per se, because of how inconsistent the values are.
CS:GO Economics 101 with Trilexium
Back onto the topic: Most expensive skin I've got is probably my vanilla Gut Knife. Used to have a battle-scarred Dragon Lore.