The summary of the story... flavor preferences vary and you can't judge a product by price alone. Sure... a lot of so-called "premium" products are highly overrated, but there are lots of others that are simply OUTSTANDING. Likewise, a lot of "cheap" e-juice is horrible, while some is pretty tasty. The key is to shop around and do plenty of taste testing.
I will say that I've found a lot more un-vapable flavors at low-cost e-juice suppliers than "premium" ones. Cheap e-juice often comes in dozens (or hundreds!) of different varieties, so there's a lot more to sort through. The flavors are often simplified and less refined, meaning you have to steep, mix, and experiment more to make them taste right. Personally, I'd prefer to pay a little extra and leave the fine-tuning to someone else. Obviously, there are exceptions to the rule, but in general, paying a little more often has some benefits. It's all a matter of preference...
Haven't tried Unicorns Milk yet... how does it compare to Mother's Milk (Suicide Bunny)? Sounds pretty similar. Right now Seduce Juice is my go-to e-juice supplier - moderately priced with an excellent assortment of premium flavors. Snake Oil is worth the hype (IMO). I also dig Jezebel...