This is an interested thread.
I have tried and enjoyed what I consider to be "premium" brands such as Hurricane Vapors and Five Pawns. Average cost per mil there is generally .75+
More often, I order from vendors such as ITC Vapes, Vape Wild and In The Clouds, whose average price per ml is less than .45, even at small quantities. I don't order from MBV, whose chemical tones in their juices really turn me off.
Are the "premium" brands twice as good? To me, the answer is "no". A bit more complex, maybe, but all in all, I started vaping to quit smoking cigarettes (which I've done successfully since Feb. 2013), and part of that was saving money on cigarettes. If I'm spending $100 + on vape juice every month, there is no savings.
The three brands I mentioned, as well as Keystone (I consider them a "tweener" pricewise, as they're at about .60/ml), deliver great-tasting juices at an affordable prices with solid customer service. The package is professional, and I don't give a damn about fancy packaging or anything like that.
Now, your experience may vary. Please know that I have no problem buying generic in the grocery or drug store, that's the type of guy I am (read "The Millionaire Next Door"), not that I'm a millionaire, but I try to be frugal