I have an eVic for home use only, big bastard but excellent. 2-3 day battery life and great hit. For out and about I use a mini eGo battery and a Kanger T4. Doesnt hold much juice but is very small and discrete!
Well I started with the eG-T and it was grand and then spent lots on extra batteries and what not and now they are all redundant since I got the eVIc. I would say spend as little as you can and see if its for you and if it is go for some decent kit that will last you years instead of months. Just M2C.
Dont waste your time with the disposable buy in th e shop shite. Spend a bit of money for some decent kit at the start and you wont have to upgrade too often. Off the smokes since Aug last year and now cant even stand the smell of them.