When i made my own i could make 500-700ml for $20. The expense is all up-front if you don't know what flavors you want or you want to experiment with recipes - the flavoring is relatively expensive if you want a lot of variety. If you're a "cherry cola" or "golden tobacco" sort, then the up front cost is about $40 (or was, 6 years ago), and you can make over a gallon of liquid at a strength of ~2.5% (25mg/l) off a single purchase of everything. you need 2 liters of PG, 1 liter of VG, and 1 liter of 100ml/l nicotine. then your flavoring.

anyhow, i buy juice now, too, but mine was better. I never used sweeteners. My current go-to is Naked Euro Gold 12mg, but i am on the hunt for a 25ml nicotine salt version of a similar flavor. (nicotine salt vs freebase nicotine, salt is more "mellow" and lets you put a higher concentration in, which translates directly to less use, as you're satiated much faster.)