It will start to even out, the initial investment is usually the most expensive. I probably go through about 5ml a day of vaping and the monthly expenses when you include battery replacements, atomizers, and juice averaging around $35 a month. If you want all of the toys, I could see that going up significantly.
The second most expensive part I found, was trying to find a good juice I could use as a daily vape. I finally found a good place, and was fortunate enough that they sell their juice in 48mg so I can cut it by a fourth and a couple of bottles will easily last me a month.
With as much as I vape, I could easily be a two pack a day smoker. At this point, I am saving over $250 a month on my habit.