hello merryman, 
from what I know, If you always on your aircon for long period of time, and everyday, 
then a inverter aircon is better because the cost savings will be more obvious. This is what I always thought to be. 
E.g, you on aircon at night daily, and also on it whenever you're in the study room, then a inverter will be a better choice? 
however, if you only on it to cool the room at night, then later on switch to fan, then a non-inverter will be preferred. 
am i right to say this?