I have just spent hours working out what I have spent monthly in a year of vaping.
I spend, on average £46.77 per month. (about $76)
If I smoked as I used to, I would be spending £51.28 (about $83.29)
I used to roll my own cigarettes.
I vape using Egos, tanks and with interesting bits a bobs and I mix my own e-liquid as a rule. So my vaping is no more expensive than my smoking was.
HOWEVER! If I modded and bought all sorts of experimental stuff and wadges of e-liquid, it would be more expensive than rolling my own baccy analogs.
BUT! If I vaped plain little electronic cigarettes with cartomisers instead of becoming a hobby vapourist, it would be much cheaper than rolling my own I think.
And all the above, is cheaper than buying packets of commercial cigarettes like some people I know who spend £200 ($324.87) per month on smoking. Wow!