Cigarettes are around $6 a pack and average use is 17 puffs. If the pack has 20 cigarettes thats 340 puffs per pack.
Vaporizers/ecigs are 300 to 800 puffs per charge depending on the quality and size, the cheapest being 300 puffs. PER CHARGE! Charge time depends on battery size. The standard is 600mah-900mah. Just like smartphones the bigger the battery, the longer it will last but the longer the charge time.
So a $20 vaporizer can be recharged for years before replacing. A pack a month for the year would be $72. The ecig savings are obvious.