Yeah, we have to keep in mind that we're discussing a very young industry; it's the Wild West out there. To argue that there's some sort of established order to dictate the objective quality of any juice based on its price point seems insane to me. What are the ingredients? PG, VG, nicotine, and a relatively small amount of food flavoring. All of those ingredients, even if you assume the highest quality flavorings, are inexpensive in the relevant quantities.
So certainly you can't argue that expensive juices simply cost 100-150% more in raw material. You might try to argue that the difference is in quality control and/or the quality of the labor, but that's a tough row to hoe simply because there's no solid evidence one way or another. If anything, MBV seems to have a much better reputation than the average vendor, vis-a-vis order accuracy, shipping times, and customer service, but that's a subjective judgment based on my reading of ECF and other websites. The fact is that we don't have access to reliable and meaningful statistics with regard to customer satisfaction in the world of vaping.
The far more obvious explanation for the wild variation in juice prices is that the industry is young, and vendors will charge whatever they think they can get away with charging for what is, by all reasonable estimates, an extremely low-cost product. Or, an outfit might charge more because the owner's doing all/most of the work himself, because he hasn't the sales' volume or experience to have stream-lined the process yet.
The looming threat of regulation doesn't help matters; many vendors likely feel that there may be no tomorrow. There is less natural downward pressure on the market because there's no expectation that anyone, no matter how popular their business, has a steady audience and thus will have a steady stream of revenue over the long term. Given a stable market, and given enough business volume, a juice vendor could probably make a tidy profit even if they charged half of what MBV does. But no one has any reasonable expectation that they'll ever be in that position.
Anyway, that's all a long way of saying that this ain't exactly Kobe beef versus a Whopper cheeseburger. The justification for e-juice price variations is almost entirely opaque to the consumer.
For what it's worth, the only generalized distinction I've seen between MBV juices and more expensive vendors' juices is that the more expensive juices more often come pre-steeped, and that's very nice -- but it's not because MBV is a second-class operation; it's because MBV sells juices to order. In other words, it's not necessarily a disadvantage for MBV. Nor is it necessarily an advantage. Some people will prefer no-muss, no-fuss, basically-zero-thought products like Halo's (one of my faves on the more expensive end of the spectrum). Others prefer the near-infinite customization that MBV offers. Still others will prefer something in-between.
Whatever your preferences ultimately turn out to be, there's a solid chance you're gonna hate a large portion of the juices you taste, regardless of the vendor, and regardless of the juice's quality.
