Hi, I'm not sure about the idea of making 1500 ml of just one flavor (are you sure you want to do that? Once you have your nicotine and vg/pg, they will be stable for quite a long time in a cool dark place, so you can mix with flavors in smaller sizes as you choose).
But anyway, as for nicotine, I wish I had a good inexpensive option. I've ordered quite a bit of 100 mg/ml from
Pink Mule, in Spain, most of which I'm freezing for future use over the next few years, as needed. But it's only reasonable because I've ordered large sizes for storing, so the shipping becomes more reasonable, and I cannot find another place that sells 100 mg/ml -- the best concentration for me now that I have to stockpile. (I normally use 36mg/ml for mixing, that I used to order from Poland, but my regular place closed, shipping was too much at other places I checked, if they even still offer this strength these days.)
For VG and PG, I'm still getting that locally in Greece, for 2€ per per 100 ml (by Atmos Lab, available at many places). I can find lower prices elsewhere, but the shipping price vs volume needed makes it too expensive.
I get flavors from different places, but mostly
Cloudhouse Vapor (the value packs; particularly for The Perfumers Apprentice flavors) in Germany, and
Chefs Flavours in the UK. I also order Inawera flavors from Poland, at
e-aromashop.
Locally I've ordered various items from a few places: fabvape.gr (where I usually get my pg/vg, and sometimes flavors), atomizer.gr for emergency flavors, wire, etc., some stuff from vaporsolutions.gr, esmokeguru.com. Local places are much more expensive, so it depends on if it's cheaper than shipping from elsewhere, and how fast I want/need the thing. Plus I've ordered from some other local places for Greek mods and atomizers.
Sadly, the problem is that it takes some money up front to get what you need, but the amount is going to be much less than buying cigarettes over time. It's so crazy that governments all over are making it a lot harder for people to quit smoking. I'm sorry this is more difficult than it should be.