There are a million places to buy juice. Typically you will get what you pay for. Your $23 30ML juice will taste better than your $8 30ML juice. I haven't really sampled the expensive stuff, and don't really plan to for a while. I didn't quit smoking because of cost, but at $23 for 30ML, I would be spending more on vaping than I did on cigarettes, which is pretty unacceptable to me.
I've ordered from Madvapes because it had this rare juice (coconut twist) that I started out with. It was close, but it wasn't the same. Madvapes also only sells 20/80 juice for the topvapor line that's the cheapest. I've ordered about 5-6 flavors from there and absolutely hated most of them except for the coconut twist and the sweet Carolina. It's pretty much a consensus that it's the only vapeable flavor they sell. Their flavors are really bad, trust me. I've had their Mad 4, Root Beer, Hawaiian Delight, and French Vanilla Tobacco. The French Vanilla tobacco they were nice enough to send a replacement for, but all these flavors were still awful up to 2.5 months before I completely gave up on them.
I order all my juice from Mt. Baker Vapor. $7.99 for 30ML with 2 flavor shots, which are apparently essential, I didn't know that when I first ordered. I received my order in 3 days going from Seattle to VA, and it's the best bang for your buck you can get pretty much. You spend $15 and they give you a free 15ML bottle sample of anything you want. They also let you customize juice concentration. Use code "beefcake11" and you get 11% off every day. Can't beat that.
Their juice sells for roughly 1/3 of the the gourmet places. My favorites are Banana Nut Bread, Butter Pecan, Vanilla Butternut, Strawbana, and Cinnamon Roll. I just ordered 6 more so I'll probably be adding to that list.