The price of the nic per ml is higher at higher concentrations, but you use less of it, so it is cheaper. Here's the math I did when I was deciding which strength to buy:
100mg/ml - 500 ml - $56.99 - .11/ml
36mg/ml - 500 ml - $29.99 - .06/ml
When I make a 100ml bottle of 18mg/ml liquid here's the total cost of nic in the bottle:
100mg/ml - need 18ml - 18 * .11 = $1.98
36mg/ml - need 50ml - 50 * .06 = $3.00
There are a couple issues in your calculation: 1) you've not accounted for the extra cost of vg or pg required for dilution and 2) you're calculating the price of 100mg nic at twice the equivalent volume used when calculating for 36mg.
Here, look at this example (prices from WL):
Goal: Make 1 Liter nicotine base at 18mg/ml strength
Using 48ml concentrate:
If using 48ml concentrate, you will need: 375 ml of nic (@48mg) and 625 ml of vg/pg
Then, to mix this, you will need to buy:
500ml of nic (@48mg) - $34.29
500ml of VG (two bottles required) - $9.49 x 2 = $18.98
Then prorate costs by the amounts actually used to get the total actual cost:
$34.29 x (375/500) + $18.98 x (625/1000) =
$37.48
Using 100ml concentrate:
If using 100ml concentrate, you will need: 180 ml of nic (@100mg) and 820 ml of vg/pg
Then, to mix this, you will need to buy (prices from WL):
250ml of nic (@100mg) - $29.99
500ml of VG (two bottles required) - $9.49 x 2 = $18.98
Then prorate costs by amounts used to get the total actual cost:
$29.99 x (180/250) + $18.98 x (820/1000) =
$37.16
So there is the proof -- numbers don't lie. Higher nic concentrations are NOT cheaper. And I have run these calculations among multiple various concentrations. Indeed, with the extra safety equipment required, high nic concentrations are MORE expensive.
So let's rid this from our vaping lore now -- it is falsehood. And is directing noobs toward practices that do not serve their best interests -- or those of this community. There ARE reasons for high nic concentrations but cost and safety are NOT among them. Noobs should be using the lowest nic concentration that meets their needs -- and certainly below 50mg/ml.
Would appreciate if others will also help get these facts out to both our membership and noobs. Thanks