Mixing your own eliquid is actually pretty easy, and once you get started, it can save you a lot of money.
This video by New Amsterdam Vape lays out almost all of the basics in a really helpful way:
Here are some great resources to buy supplies:
Flavors, VG and PG
Note that nicotine is an addictive and dangerous chemical that should be handled with care, only
after educating yourself on the risks and procedures for handling it safely.
Reducing and ultimately eliminating nicotine from your mixes should be your goal.