Define insanely. A lot of the smaller popular artisan shops charge around $12 for 30ml. That gets high quality ingredients, a good mix.
At moderately heavy
vaping on a standard pv that is a 10 day supply. At high voltage I run about 6 ml typical, but that is more than many vape.
A sell of $12 is about 3x the base cost of material (for me, as a diy person), but there is the time and effort to come up with the mixes, actual mixing, overhead related to setting up and maintaining a web presence, material ordering and inventory tracking, credit card processing fees, the simple fact that the vendors are doing this as a living, need to make a profit. Vendors with brick and mortar presence have much higher overhead.
Net, I'm happy to recommend the vendors I do. Some of the shops that charge much higher prices beat me, but if people are willing to pay the price, so be it. In the hardware side you will see similar variance, certain products that people are willing to pay much higher prices for than their basic cost of material and production.
I originally calculated my own vaping cost as about $2.50/day, including hw, eliquid, shipping instead of my old pad smoking habit. Since I've switched to a pair of decent vv mods, my overall cost has dropped to about $2/day (the mods are workhorses).