Yes, you're overlooking how easy this is on a larger scale. Suppose I was Ralikar's Johnson Creek and I wanted to start my own secret recipe and make it really easy to mass produce:
100mg nic 100% PG is $57 at WL for 500 ml...
1500ml of PG from WL is $30
Making a 25% nic PG solution of 2000ml
10% VG is about $5
Making 2200 ml of base 22.5 nic
Now if you use a 15% secret blend of Capellas which is way expensive 120ml (4 oz) costs $20... so you'd need about $60 (3 bottles) in flavors...
Which gives you 2530 ml of juice...
Which gives you 84 bottles of juice
At $20/bottle for 30ml you've made $1680
-1$/dropper bottle...
So for $209 in cost on the easy to make side you've made $1600 in product. And customer pays for shipping. Once you know the ratios, you probably want to test your nic from the supplier, dump all into sealed vat at once and steep.
You're making a ton of cash/batch. Even more with bulk discounts.
Hmmm... this DOES make me want to make "Ralikar's special vape"... Hmmm....
Easy on a larger scale?
Now that you're the size of Johnson Creek you need a million dollar building (low estimate). If you buy the building that's considered income. If you rent the building it's money down the drain but you get to write it off as it goes down the drain. Their building is 24,000 square feet. They lease it. Figuring it at $11 square foot (which I think is cheap, probably more like $15-$20) you have to come up with about $250,000 a month in rent.
You have about 30 employees full time and they need to make enough money to live. There's $1M a year plus another $120,000 in your part of their social security.
Don't forget your insurance. If you have employees messing with nicotine that's going to be costly.
Your customers don't pay the shipping in and everything that goes out had to come in.
You also have an excellent customer service guarantee so they don't pay for juices they don't like or the shipping back and forth of the juice they didn't like or the one you replaced it with.
You really think you're going to make it big mixing the same flavors everyone else makes? No, you'd better work with the flavor companies to get some exclusives. That means more money going out because they're not making exclusive flavors unless you're making it worth their while.
I'm sure there are a lot of things I haven't thought of because I've only been in or run very small businesses. But I can tell you're thinking like a countertop mixer and trying to apply that to a major player.
Yes that small local DIY guy charging $1/ml is making profit, but he doesn't have enough business to be making much money.
As the business grows so does the overhead. Sticking with Johnson Creek, they got big enough to get on the FDA radar a year after opening.
I can make wine at home with my own fruit for next to nothing. That may also sound like a high profit industry until you start looking into it and trying to make enough to make the requirements pay for themselves.