Is there a savings? Most definitely.
You cant really get a like for like comparison because and E-Lites cartomiser is not like a Boge SR or LR cartomiser, they may do the same thing but there are differences.
You have to take into consideration, the capacity difference, the OHM of the coil that heats the liquid, the voltage it is being vaped at.
All these things factor in.
The best peice of advice I can give you, if you are concerned most about saving money, you need to get away from restrictive devices which do not allow you the options that are available to you.
I make E-liquid at the cost of roughly 2-3p per ml. I use a rebuildable tank which costs me about 3p per new wick and coil (if even that high) and a rebuildable dripping atomiser thats about 2p per new wick n wire. Replacing them weekly or bi-weekly, sometimes monthly.
My major costs now consist of 3 things, Nicotine Base Flavour Concentrates and batteries
Last year I spent £16.45 per week on vape gear versus £12 per day on smokes. This year I reckon I will be down to about £5 per week.