I usually smoke a pack a day, and cigs are $5 a pack here, so about $150 per month. I just got a lavatube (and batteries and charger) for $100, and 60ML of juice and several cartos for another $50. The juice should last me all month (if not more), but I will probably have to buy more cartos, though I've already gotten a few days out of the first one.
The first month of replacing analogs with the LT will be more expensive, but I'll be saving about $100 per month thereafter. And it tastes better, and I can do it inside, and I remember after using the Ego to quit for a few months last year that I felt much better after the first couple weeks without a cigarette. I just don't see any downsides with vaping. Unless you're buying a new mod every month, which I may be doing for the next few months. I want a small mod, so I'm thinking of getting a Roughstack, and maybe a GLV mini at some point after that.
Anyway, I'm rambling. The point is that the upfront cost is certainly higher, but the long-run cost should be quite a bit lower, depending on your spending habits.