Congrats to the OP for entering the fun world of DIY! I've been mixing my own e-liquid for a little over a year now. Typically I buy nicotine base in quantities up to 250-500ml at a time these days, PG and VG by the boatloads as well. Flavorings.. I don't even want to think about how many I have. I tend to mix for my entire family of vapers which is about a half dozen people. We all pitch in on the supplies, keep em dark and keep em cool and they last a long time. I do highly recommend you invest in child resistant caps for your bottles though, especially if you have children around. You can definitely save a ton of money, but to be honest, at first you will not. You'll be ordering every flavoring under the sun to try out, which is normal, and the cost will probably go up. After a while you'll settle into a few mixes you really like and you'll start to save some coin.
Enjoy!