once i found some diy recipes that i enjoyed, i made a pair of 120ml, and the cost savings from those two bottles alone covered all the ingredients and equipment (beakers, stirring rods, scale, bottles, etc). diy is especially worthwhile if your device guzzles juice like my geekvape griffin tank does.
diy or die on youtube is a great resource, here's one of the recipes i make regularly: https://www.youtube.com/watch?v=QlI8CvT8SCA