I have only ever used the nic from RTS vapes
The different levels of nic increase in cost as you go up ie: 36mg 60ml is $6.95 compared to 100mg 60ml is $14.95
so the higher nic is a better deal
However (big however) if you accidently spill 36mg nic and your pet (or small child) gets into it will certainly make them sick but if the same thing happens with 100mg it will more than likely kill them (a small amount on your skin will cause major illness)
I recommend reading all the stickies in the diy subforum if you are going to mix it yourself
But if you want to
buy premixed
juice in flavors and dilute it down as you work on quitting your dependency on nic ie: starting with 24mg flavored and adding 0mg nic of the same flavor in increasing levels that works great (Tasty Vapor has a 4 ounce doubler 0mg nic that makes this scenario very cost effective - 1 ounce = about 30ml)
see my signature below to see how cheap DIY can be per month