I'm kinda looking for a new phone, should be super cheap (so a used one would do), I wanna modify it to be secure (proper encryption, VPN, etc.), very good battery time and not very big (more like 4"). I have been looking at the Lenovo P2 a lot, but I'm afraid my current phone will die before I have enough money for that one (I'm a broke trainee yay).

So what do y'all have or can recommend?