Price includes: Clean space (hopefully), storage space, labor, equipment, inventory, record keeping, taxes fees and permits as applicable, utilities, office and cleaning supplies, packaging, insurances, promotion (advertising, social media, samples, etc.)..and there's more. There's always more! Lol
So when you buy from a vendor you aren't just buying juice, but paying for everything that goes into the convenience of having someone develop the flavors, mix it for you and deliver it to you, all while maintaining a clean environment and doing what's necessary to keep filling ypur orders tomorrow and the next day.
And hopefully after paying everything and everyone they also get a profit, cuz why else go into business at all?
Then there are different business models. A vendor like Mt Baker sells at low margin but high volume. Smaller "boutique" vendors sell much smaller volume so they need a higher margin to pay the bills. Sometimes it's due to marketing or branding factors, such as vendors who use very expensive, attention catching packaging as a selling point but it inflates the price. And then there are those who use price itself as a marketing tool, choosing to target a certain segment of the extremely low end (dangerous if you're not EXTREMELY savvy, see Lucky 7) or extremely high end market.
So yeah...it gets complicated. Choose a price point and stick with it or DIY if you can't find something you like in your budget. Not sure what else to tell you.