As long as people are willing to pay $15-$20 for a 30ml bottle of juice, there will vendors who will offer it at those prices. They charge what the traffic will bear. I personally don't mind paying those prices; I like certain juices and even at those prices, juice only costs me a spend a fraction of what I used to spend on store-bought smokes. Can a smoker save money by rolling his own, or a vaper by DIY'ing? You bet, but I doubt a majority of them ever will, unless of course the gang of criminals in DC leaves them no other choice.
Just because you paid $100 for a carton of smokes dont mean paying 20 bucks for a bottle of juice is a deal.