Electrical help

I need some technical knowledge from any one who knows there electricals… I have a 1965 VNB its main power source runs off the magneto: lights,horn,ect. I am adding some accessories that need power.
I have thought of running them off a secondary battery. but that battery needs a charging system(stator,regulator,etc). does any one know a way of a charging system for a battery that wont burn a hole in my pocket?
or is there a way of useing the stator as the charging system?