Kinga, it was great to read, even after 4 years, even if the prices are completely different now, but the main point is still that vaping is still cheaper DIY/making your own.
Personally, I can’t really comment on the prices, only that when I smoked cigarettes, I went through 1.5 packs a day. With vaping, I have a 4ml tank on paper that I refill on average 4 times a day, but this is usually less or more. When I started vaping, like everyone else, I bought various flavors, then better and better atomizers, devices, but luckily I quickly found my go-to hardware. Thousands of liquids, then slowly I found my favorites, but as usual, curiosity drove me and new ones came. 
The point is, I can’t quantify it (although they always ask), but I think a lot when buying and it lasts for 1-1.5 years. Unfortunately or fortunately, I discovered a favorite that is only available as a longfill (Adams Vape), so expensive or not, I need it and will need it. Of course, independently of this, luckily there are also aromas that I like. So I can’t quantify it, and maybe it’s better that way because my eyes might pop out Currently, 47 longfills were resting in the fridge, unmixed, which I bought back in October last year.