Brother if you are looking an inverter ac for good cooling and lower billing you should only look for Branded Air Conditioners, because Brands like Daikin, General, Panasonic, Lg, Samsung have the capability to quickly cool and comparitively low billings than our local brands like Haier, Gree, Orient, Pel etc.
As far as the billing concerned no body can give you exact amount but it depends on your usage, working hours, the temp you set, outdoor weather.
Incase if you set temp 27/28 it should be achehived soon thus should start consuming low electricity.
But much more depends on your room location, room size, air conditioner size which you will use.
Hope it helps you little bit