It's impossible to scientifically say for sure because there's too many variables.
However, I think it's a safe assumption that you'll have comparable methods/habits with an e-cig that you did with cigarettes.
My observation based on satisfaction:
3mg of vaped nic. ~= 1 full flavor cigarette
so,
1ml of 18mg/ml ~= 6 cigarettes
1ml of 12mg/ml ~= 4 cigarettes
1ml of 6mg/ml ~= 2 cigarettes
When I got good hardware, I was using about 4.5ml of 20mg/ml a day. 90mg total. 90mg/3mg = 30 cigarettes, about right, I was smoking ~35.
I noted a few other peoples comparisons between amount they smoked and amount they
vape, and this seems be a good ballpark figure.
I save as bunch using DIY liquids. My vape budget is $10 a week and I still have enough to get new shiny stuff occasionally. Was spending about $50 a week on cigs.