I have more than doubled my spending in the last 4 months as compared to smoking.... BUT, I have built up a stash of juice that will last maybe a year or more, I have all the devices I need for a year or more (the Provari and Cobra will last hopefully years), I have enough rebuildable materials to last a year or more, and now I can sit back and watch the savings accumulate for the next year or more!
When it comes time to replenish juice and wick/wire, it won't cost very much as those are the cheapest inputs.I may get into DIY at that point too, and it will be even cheaper.
I started with a Redds kit, Twists, and then Provari and have a Sigelei Zmax coming soon. I use all of the devices still so I am happy with the way I purchased. I would recommend buying small at first, but then go big once you know you are going to stick with vaping ( say after a month or once you have the funds). Buying every next step up will cost you and there is likely little difference between the steps.